Is there a way to set fire tick on in a limited area in bedrock vanilla

I'm not a command block master, and I don't even think that a "limited area" is possible without preventing players using flint and steel at all or causing extreme lag and crashing due to bedrock's limitations.

However, if the entire realm has the setting off, the settings screen of the realm has interaction with it disabled, even with the realm shut off. To do this you need to type;

/gamerule doFireTick 1

This will enable firespreading for the entire realm, bypassing the settings screen's limitations. Just remember you must be Operator Ranked, have the "Commands" Privledge or be the owner of the realm for this. If not, ask the owner for them to enable it.