Living Trust Not Being Honored

My uncle was named as a beneficiary when his client passed. Essentially 50% of all assets, after expenses and distribution of funds to the deceased’s named charities.

The next of kin is not distributing money to the charities stated. They are also not producing receipts for the expenses they stated they’ve incurred, during the estate sale.

They have only offered my Uncle a sum, which he believes should be nearly double.

Should he retain a lawyer and sue? Or is there another route he can take as to ensure the living trust is fully and honestly executed?

Thanks for any help you guys can provide!