All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
The registration of a house under the name of a certain person does not transfer the ownership from the real owner to that person. If your financial contribution in those two houses was intended as a donation to your mother, then they have become hers, and you have no right to demand it, but if that contribution was not intended as a donation to your mother, then you have the right to demand it.
On the other hand, if you paid that contribution as a partner in the two houses, you would have an unspecified share in them equivalent to your contribution; otherwise you would be entitled to the amount you paid to your mother as cash money, and the mother's share is hers. If she dies, it will be an inheritance to be distributed among all her heirs, including your brother. As regards your share in the two houses, then it is yours and not included in the inheritance.
In any case, you should divide and register the rights during your mother's lifetime in order to eliminate any reasons for dispute between the heirs.
Allaah Knows best.