16 June 2015
Payments from sisters and mother's account may be treated as gift. Gift from relatives is exempt therefore it will be exempt. It will be better to execute a gift deed in favour of both brothers and it may also be mentioned in the gift deed that the gifted amount will be paid directly to the builder's account.
17 June 2015
Dear if you do not want to execute gift deed then you can show the amount paid by sis & mom as loan in your personal balance sheet. As getting gift deed registered seems a good option orally in practice it take lot of time & money.