1) Your uncle and your father are rightful heirs. There could be others. Although " adverse possession " could assist your case, depending upon the entirety of facts and claims.
2) But, unless proper partition has been done by " metes and bounds " - that is, everyone's area has been clearly agreed and demarcated- locking as you claim can not be done.
3) Your father is the present possessor and anyone has to go through proper procedure to disposess him to any extent and of any share, although sharing by other heirs can not be denied. He could try reporting the matter to police and have the lock broken in their presence . Others could also stand witness to avoid counter claims of stealing etc.
If there are any notices, agreements, documents etc that could be a different matter then, please note.
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