Style files for court forms: motions, affidavits, etc?

Generally, dividing the page into rectangular blocks or frames, then filling them with boilerplate-text and macro variables, is the usual way to go.

However, two names, a date, and a set of items (clauses/reasons) is the structure of a bibliographic entry, which suggests the idea of using biblatex and its datamodel power: ... each cause being one bib entry, with reason sets being per-entry:

Overall view;

Detail:

Top half:

Bottom half:

Feasible.

<< Edited: Original version of answer said: "Some minor tweaking still to do." Tweaking has been done: border added (via TikZ); blank line before sub-list removed; saveboxes used for names and date; signature locations shifted slightly, for more balanced appearance; and cellspace package for a touch of space under hlines in a tabular. MWE code updated. >>

Plus, page size, and fonts, need to be set as appropriate/required.

The box decoration can be done with tikz, or an eso-pic on the background layer.

MWE

begin{filecontents*}[overwrite]{jobname.bib}
@xdata{cc6,
courtname={CIRCUIT COURT OF ILLINOIS},
courtrank={Sixth Judicial Circuit},
courtjurisdiction={Champaign County},
}
@xdata{lsk,
clerkname={LSK},
clerkaddressa={address line 1},
clerkaddressb={address line 2},
}

@misc{A01,
  petitioner = {D Ducke and M Mousse},
  sepdate = {2020-09-16},
  xdata = {cc6,lsk},
  template = {standardu},
  reasons = {irrdiff, imprec, livsep, waitwo, divprop, wairig, volact,  ackatt,},
}
@misc{A02,
  petitioner = {Jack Spratt and Jill Spratt},
  xdata = {cc6,lsk},
  sepdate = {1520-02-14},
  reasons = {irrdiff, imprec, livsep, waitwo, divprop, wairig, volact,  ackatt,},
}
@misc{item1,
itemdescription={item 1 description},
}
@misc{item2,
itemdescription={item 2 description},
}

@misc{irrdiff,
itemdescription={That irreconcilable differences have caused the irretrievable breakdown of their marriage.},
}
@misc{imprec,
itemdescription={That all efforts at reconciliation of the differences between the parties have heretofore failed or future attempts at reconciliation would be impractical and not in the best interest of the parties.},
}
@misc{livsep,
itemdescription={That the parties have lived separate and apart for a continuous period of more than six (6) months prior to the date of this Affidavit, having separated on or about usebox{sbdate}, and have remained living separate for all times thereafter.},
}
@misc{waitwo,
itemdescription={vspace{-itemsep}vspace{-baselineskip}begin{enumerate}[topsep=0pt]item That each of the parties hereto expressly waive the requirement that the continuous period of living separate and apart be in excess of two (2) years in order for the court to enter a Dissolution of  Marriage based upon irreconcilable differences which have cause the irretrievable breakdown of their marriage.item  Each of the parties further stipulates that the requirement shall be reduced to a period of only in excess of six (6) months rather than in excess of two (2) years as provided by Section 401(a)(2) of the Illinois Marriage and Dissolution of Marriage Act. end{enumerate}},
}
@misc{divprop,
itemdescription={That the marital property amd debt belonging to the parties has been divided according to the terms of the written agreement of the parties filed with the Joint Petition for Simplified Dissolution of Marriage    in this cause, and that the parties have executed all documents required to carry out the agreement.},
}
@misc{wairig,
itemdescription={That the parties waive any right either may have to a bifurcated hearing in this cause.},
}
@misc{volact,
itemdescription={That each of the parties represents that the signing of the Affidavit is their individual, sole, and voluntary act.},
}
@misc{ackatt,
itemdescription={That each of the parties accknowledges that he/she has the right to consult with an attorney and wither done so or has freely chosen not so do so.},
}
end{filecontents*}




begin{filecontents*}[overwrite]{courtform.dbx}
DeclareDatamodelEntryfields[misc]{%
courtname,
courtrank,
courtjurisdiction,
petitioner,
reasons,
clerkname,
clerkaddressa,
clerkaddressb,
itemdescription,
sepdate,
}
DeclareDatamodelFields[type=list, datatype=name]{%
petitioner,
}
DeclareDatamodelFields[type=field, format=xsv, datatype=entrykey]{%
reasons,
}
DeclareDatamodelFields[type=field, datatype=literal]{%
courtname,
courtrank,
courtjurisdiction,
clerkname,
clerkaddressa,
clerkaddressb,
itemdescription,
}
DeclareDatamodelFields[type=field, datatype=date]{%
sepdate,
}
end{filecontents*}




documentclass[legal]{article}
usepackage[margin=1.5cm]{geometry}
usepackage{enumitem}
usepackage{cellspace}%for space under hlines in tables
setlength{cellspacetoplimit}{0.5em}
%usepackage{xcolor}
usepackage[english]{babel}%for American date format for biblatex
%
newsavebox{sbdate}
newsavebox{sbpeta}
newsavebox{sbpetb}
%
%
%for the frame
usepackage{tikz}
%
usepackage[datamodel=courtform,
sepdate=comp,
dateabbrev=false]{biblatex}


addbibresource{jobname.bib}

DeclareFieldFormat[misc]{itemdescription}{#1}

newcommand{entry}[1]{
    item entrydata{#1}{printfield{itemdescription}}
}

DeclareFieldFormat{reasons}{
    begin{enumerate}[topsep=0pt]
        forcsvfield{entry}{reasons}
    end{enumerate}
}


DefineBibliographyStrings{english}{%
andothers = {unspace},%remove et al. from first name, and the preceeding space
}

DeclareFieldFormat{courtname}{hfillmkbibbold{#1}hfill }
DeclareFieldFormat{courtrank}{hfillmkbibbold{#1}hfill }
DeclareFieldFormat{courtjurisdiction}{ hfillmkbibbold{#1}hfill }



DeclareCiteCommand{citeitem}%
{}
{printfield{itemdescription}}
{}
{}

DeclareCiteCommand{citeform}%
{}
{%
%top right corner of frame border:
hfill tikz[overlay,remember picture]node[xshift=1.2em](ttr){};
%the form:
bfseries
savebox{sbdate}{printsepdate}%for re-use
savebox{sbpeta}{printnames[][1-1]{petitioner}}%for re-use
savebox{sbpetb}{printnames[][2-2]{petitioner}}%for re-use
begin{center}begin{tabular}{c}
printfield{courtname}%
%
printfield{courtrank}%
printfield{courtjurisdiction}%
end{tabular}end{center}

begin{tabular}{Sl}%S for extra vertical space
IN RE: THE MARRIAGE OF:

usebox{sbpeta}%
hline CO-PETITIONER%

 
usebox{sbpetb}%
hline CO-PETITIONER%

end{tabular}
begin{tabular}{l}


%

%
and 
%

%
end{tabular}
begin{tabular}{r}
mbox{hspace{2em}}

)%
)
)%
)
)%
)
)%
end{tabular}
begin{tabular}{c}


%

%
hspace{3em}Case No. underline{hspace{12em}} 
%

%
end{tabular}

begin{center}begin{tabular}{c}
JOINT AFFIDDAVIT REGARDING SEPARATION OF THE PARTIES, DIVISION OF
PROPERTY AND DEBT AND WAIVER OF BIFURCATED HEARING
end{tabular}end{center}

mdseries
Co-Petitioners, usebox{sbpeta}, and usebox{sbpetb}, being first sworn on their oaths, depose and state as follows:

printfield{reasons}
vfill
 hspace{5em}
begin{tabular}{Sc}%with vertical space
hspace{40em}
hline (Co-Petitioner's Signature)
end{tabular}
hfill
begin{tabular}{Sc}
hspace{4em}
hline (Co-Petitioner's Signature)
end{tabular}hspace{7em}

%bottom left corner of frame border:
tikz[overlay,remember picture]node[xshift=-2em](bbl){};

begin{center}begin{tabular}{c}
printfield{clerkname}
printfield{clerkaddressa}
printfield{clerkaddressb}
end{tabular}end{center}

%draw the frame:
begin{tikzpicture}[overlay,remember picture]
   draw[black, thick] (bbl) rectangle (ttr);
end{tikzpicture}
}%
{}
{}
%========================

renewcommandthepage{}% remove page number

begin{document}
nocite{irrdiff,imprec,livsep,waitwo,divprop,wairig,volact,ackatt}
citeform{A01}
newpage
citeform{A02}

end{document}

---

Edited to add: The core methodology, about using xsv-list fields to call in other bibentries, was adapted from here: Biblatex: Citing complex nested unpublished sources a question about referencing components of an archive.

The methodology can be adapted to apply to exhibit lists, appeal books, skeleton argument authority dependencies, exhibition catalogues of art galleries, collectibles of a TV show (or stamps or coins), archaeological site finds, reading (or activity) lists for students and arranged by topic, year and level, and so on.