My husband has just completed the shloshim for his mother and still will not shave or have a hair cut. People have told him too but he thinks it is because i asked them too. It is causing a problem with shalom bayit for me.
As long as he genuinely looks disheveled, and people around him mention to him that he looks unkempt and needs to be groomed, he may take a haircut. This includes from a spouse or friends or others.
SHulchan Aruch Y:D 390:4