Need advice for dispute flat

The Situation:

Father passed away 10 years ago and mother passed away 2 years ago.

The flat is on 3 brothers name, lets call this flat as parents flat.

Two brothers have their own homes and live at different locations. Their documents like Aadhar and passport have locations to their own home respectively and not their parents flat.

The youngest brother lives in the parents flat with this family. Now the building has been brought by a private developer and is going to redevelop the building while following DCR 33(7) guidelines by MHADA.

When redevelopment procedure starts, MHADA will come to take the measurements and will prepare the occupant list, if your name is in this list your name would be on the property card. The two brothers not living there made new proofs, by opening a bank account and updating aadhaar details for the parents flat address. These proofs were enough for MHADA to register them as occupants of the flat along with the youngest brother who has been living their for 15 years.

The Problem:

The occupany list was sent to the developer along with NOC. When the younger brother found out that both of his brother's names are also registered as occupants, he filed a complaint in MHADA and sent a notice to the developer and both the brothers and called for a hearing. While the notice doesn't why there is a hearing, we suspect that he would want us to show prove our occupancy of that flat. The developer with whom we have good professional relations, suggested us to gather as many old proofs as possible like marriage certificate, voter id for that address. But this is very difficult.

If we arent able to produce these proofs, MHADA will rule in the favour of the youngest brother and entitle him to be the sole occupant of the house and we would have to go to the court to fight against MHADA proving that while we arent occupants we are tenants of the flat and hence should have our name on the property card. This procedure will be length and time consuming and ofcourse money consuming, futher more the rent money given by the developer will also be given to the youngest brother only.

The only old proof we have is Rent Receipt but MHADA doesnt accept it as an address proof.

Any suggestions you could give regarding :-

1) what proofs can we gather and where can we get them

2) if mhada rules in the youngest brothers favour, how can we get a stay order, can we stop him from receiving the rent money

3) any other suggestion

Thank you for all the help and your time. God bless you.