Gift deed made without our will

I Mohd shafi Brother : Gulzar Ahmad (Younger brother) Mother : zeba bano. ( matrilocal residence) Maternal uncle : Gh. Ahmad dar. ( Handicapped) Our maternal uncle was handicapped, so one of his sister (our mother ) was married matrilocal residence to keep the house functional (to work ,earn ,etc) This person was later on married but had no children. Our mother died few years ago ,& in 2019 our maternal uncle also died .After his death we came to know that he had done a gift deed in favor of his wife ,the piece of land he gifted was not his own property fully ,it was half his & half ours. As per record this piece of land is mentioned as ( آبادی دہ ) land for living purposes. That piece of land was under his possession ,we didn't give it to him ,but it was only as he had been telling us his entire life that my whole property is for you both,so we didn't try to take our share from it, thought that it is all ours. At the time gift deed was made unfortunately my younger brother was witness there along with a friend . Without knowing what maternal uncle was doing he blindly signed as witness . What are the possible solutions for us to challenge this gift deed. Thanks