A. In your case, your grandmother acquired some property through her mother would be treated as her absolute property under Sridhana as per the Hindu sucession Act.
B. Being an absolute owner of the property that she sold the same to your uncle. Whether it is registered or not is still arcane? However, it can be presumed that it might be exeucted by way of registration after verifying your question i.e, appeal preferred over lower court verdict.
C. Therefore, Sale Deed executed by grandmother is vaild and your father cannot question the same. And Court will not give any stay order in favour of your father.