How can wrong actions be rectified?

It will be a lengthy question but it is necessary for its nature. A couple (my khala and khalooo) had six children, one son (eldest) and five daughters. One daughter is mentally distorted. The father MF died when youngest daughter was not matured enough. The second last daughter was disabled. The four elders decided and transfer the house in the name of mother by signing an agreement on stamp paper. Keep in mind they ignored the last two daughters and they have not signed any agreement. The house came under the name of Mother. The mother beacame paralysed and only youngest daughter was serving her in all means. The two other elder daughters are married and settled with their families. They were not having good contacts with mother and others. In the meantime the third daughter was also expired leaving behind a son. The last two daughters were living with mother in her home, as mentioned one is disabled and youngest was serving both mother and disabled sister in all means. In next move the sons insist mother to give his share from the house. He said that if it will not be done then he will now allow the marriage of the youngest sister in the house and start making trouble. He was pressurizing mother and he prepared the paper and took half portion of the house and transferred it in his own name. That means mother transferred the half portion in her son’s name. Now half portion left in the mother’s name. Then youngest daughters marriage took place. She lived with her husband in mothers house to take care for her and also to take care of disabled sister. Now the son is looking on the other half portion which is held with mother. Mother understood his intention and his behavior was not good with his mother. Mother became too ill and even she was not able to move to bathroom and only youngest daughter was taking care of her. Mother asked her and her husband to transfer this half portion of her home in their own name. It seems that husband of the youngest one was not greedy and wanted to give this portion to Mosque, the main mosque was just in front of their home. He told me all this and looking that what is my opinion. I told that whatever was happened was not correct at all. The transfer of house in mother name by ignoring the names of last two daughters in the agreement. Then half portion was given to the son. Now remaining half she wants to give to you. What about other two daughters, where is the share for them (no matter they are not having good relationship). I asked them to call two others sisters (elders) and mention about your intention, if they agree then you may do or as mother wants to transfer in your name. But their consultancy is must. The son was waiting that as soon as his mother will pass away he will put his claim in the remaining portion. The youngest daughter moved to other (city) due to work of her husband and they took mother and the disabled sister with them to take care there. They locked the house. No one did anything for transfer and recently mother has passed away. The son is there and wants to take over at the house. He doesn’t want to sell it and wants to give on rent or whatever else. If they agree on sale then shares will go to this son also or not as he has taken his share but not written anywhere that he has taken his share and will not claim in the remaining part. I think legally he can claim but according to religion he should not if there is any understanding. In view of all this what action would be correct. What was the actions taken wrongly earlier. In case of wrong action how it can be rectified and what action children should do to rectify.