Possessions Of A Deceased Acquired Years Later

The container found in your late father’s belongings is a clear indication that it belongs to him, as the funds were in his possession and no one has claimed any such funds from his demise until now. 

However, he had excluded a certain amount from it by attaching a note (as a confession) which states that a certain amount belongs to your grandparents who are now late. 

Based on the above, the funds belonging to your late grandparent’s estate should be handed over to the executors of their estate, whilst the funds owned by your late father should be distributed amongst his heirs as stipulated in Shariah.