Annoying mother in law.

Ladies is it normal for my mother in law to call her son 6 times a day. When he doesnt answer she calls me and if he or i dont answer she gets butt hurt. It's fine once a day but 6 times. We both had told her in a nice way but she doesnt seem to get it. My husband only answers once because he said he wants to tell her hes fine but once for her isn't enough