Conflict on land ownership

My maternal grandmother gave her lot in Cainta to my mother and to my uncle (now in Canada) in the early 1990s. The transfer of title was halted in the 2000s due to the diagnosis that my mother had cancer. The processing was set aside so that she could deal with her sickness wihtout much stress. Unfortunately, she died in 2013. Since then, the transfer of title still did not push through since we, her legal heirs, and my uncle in Canada did not see the urgency to do so since we are still trying to cope up with our loss and besides, it was a family deal so we weren't much in a hurry. In mid-2016, my other uncle came up to us and said that he wanted to get the lot in Cainta for him to be able to build his house. We objected, but he insisted that the lot was still under my grandmother's name and that she has the right to decide whom to give it to. He continues to argue this but we, the legal heirs, my uncle in Canada and other members of the family object to his proposal. Now, he wants to proceed since he argues that we cannot do anything about it anymore since my grandmother decided to give it to him. What legal remedies could we, as legal heirs, do to prevent him from grabbing the land from us?

Thank you.

Are there any DOCUMENTS concerning gift or will?

If will, then ALL hiers get shares anyway, but some can be reduced.
If gift, I don't know if other hiers can demand a share anyway.

"What legal remedies could we, as legal heirs, do to prevent him from grabbing the land from us?"
If it's titled, he can't just do that.

I asume no legal process is done to decide what the hiers get. Corect?

The Deed of Donation was not notarized but there was an extrajudicial settlement among the siblings that they waive their right in favor of my mother and my uncle. Though document is not with me anymore, it was handed over by my grandmother to my uncle claiming to get our share. On the title, it is still under the name of my grandmother since my mom wasn't able to process it, though the intent was there. As my other uncle claims, since the title is still under my grandmother's name, my grandmother has the right to decide whom to give it to. But I think otherwise. What could be done with this gridlock?

Did the uncle, who want to build house, signed the document waived his rights too?

Logicaly your grandmother can't give it away to some else, if she had given it away 20 years ago,
BUT the missing notarisation make a problem. I don't know if that it can be canceled by that.
Have you/your uncle tried to get the old documents notariced NOW?