Tax benefit on home loan of under construction as well as ready possession property

I am from Pune, India and working in Ratnagiri.

I have purchased a under constructed flat as a Co-Owner in FY 18-19 in Pune. Possession will be after four years i.e. 2022. First Owner is my wife. We both have taken home loan. Since being the 2nd Owner of flat, my actual home loan EMI will be started after two years. Since loan yet to start and under constructed flat, i am not able to get tax benefit of interest upto possession.

However Now i am planning to buy another 1 BHK ready possession flat with home loan in Pune.

Now question is which will be my first property ? The under constructed flat or the Ready possession flat ?

If i availed the new home loan on ready possession flat and the interest paid upto 1.50 lacs, can i get the tax benefit ?

If yes currently i am paying tax around of Rs. 1.00 lac after 80C, Medical insurance, NPS, etc, do i still need to pay a tax of Rs. 1.oo lacs.

I am also getting tax benefit of HRA since I am working in Ratnagiri. Will it be continued as earlier ?

Kindly advise on this at the earliest.