What is the ruling on receiving money sent annually from a family that used to reward scholars, even after my husband finished working for them as a private tutor?

There is no harm in accepting these funds, whether they are a grant, a gift, or a reward. It is praiseworthy to reciprocate them, as the Prophet, peace and blessings be upon him, used to accept gifts and reward for them. He said: "Whoever does a favor for you, reciprocate him. If you do not find anything with which to reciprocate him, then supplicate for him until you know that you have reciprocated him."