You should seek professional legal and tax guidance for this scenario (one legal issue is how the account was held (e.g., tenants in common, joint tenants, et al).
Generally, though a return for your uncle should be filed and the proceeds reported as being received on his return as nominee for your grandmother and your uncle's estate (assuming there was no right of survivorship).
The estate and your grandmother would then report the allocated share of the proceeds/gain on each of the returns (1041 and 1040).
Again, seek professional assistance.
