Firstly you must be aware of the legal fact that the house belongs to your grandfather and during his life time nobody can force him to transfer his property or even make a partition and allot any share to anyone. He is the only and absolute owner hence he can do only whatever he feels right.
Now in this family arrangement, if your grandfather is okay to allot your mother her share, first you get it transferred on her name by a settlement deed registered on her name. As far as your paternal uncle's share, if he is ready to sell his share, you may buy it on your name, please make sure that you should acquire it only through a registered sale deed and not by any other mode of transfer namely, settlement or gift deed or will etc. These are liable to be disputed at a later stage and you may have to run behind the litigation unnecessarily.
Since your grandfather is adamantly refusing to transfer his ground floor share now, dont agitate his decision, he may be sentimentally affected and the impact may be more adverse, hence allow him to devolve on his own decision without objecting to it. If he is saying that he may bequeath the property by a will in your mother's favor, wait and watch the developments. You should not make this as a destination, especially if this property has to come to your family nobody can stop you from acquiring them, so allow things to happen in the legal way for the present.