The matter what you have posted is not a fit case to be discussed here. This involves housing society, housing federation an HUDCO, If the society approached housing federation, then the federation entered into a mortgage with HUDCO for mortgage loan.
Now the society has not made registration in the name of buyers, therefore the buyers are literally not bound by the bank terms until there is a tripartite agreement between society, buyer and bank. Whereas the federation already availed loan, so who is the defaulter to HUDCO now?
The entire matter has to be studied along with the relevant papers, hence your own advocate, who has sen all the papers and is in full knowledge about the transactions and dealing shall be right person to give proper opinion. or you can revert with his opinion for a second opinion with accurate details, you shall be rendered with proper opinion and suggestions therein. .