Who checks up on lawyers who stall paying inheritance to the beneficiaries?

The beneficiaries are those with standing to complain. You should start by contacting the lawyer to ask for the reason for the delay. There may be a legal factor that you are not aware of. The debts of the decedent must be paid. It takes some time to obtain final bills showing the amounts due for various expenses and costs. There is a statutory period that varies from state-to-state during which creditors may make a claim against the estate. The assets can't be distributed before that period has passed. You need to see if that statutory period has passed. The estate tax forms must be filed and taxes paid if necessary. You can request the file at court and review it to see if all the necessary filings have been made. If the time for all of the above has passed and the attorney isn't in the process of making the distribution then complain firmly to her/him. Be polite but assertive and business-like. Ask when you can expect a check. If you don't receive a prompt response, an apology for the delay and a date by which you will receive payment then make it known that you will complain to the court (a motion to compel the attorney to make distribution) and send a malpractice complaint to the state board of bar overseers if distribution is not made immediately.