First of all, what you said in the title is, bad habits . It is good that your daughter-in-law is asking your son to change his bad habits. If your son understands that your daughter-in-law is doing this for her own good, and he is willing to change, then we suggest that you don't have to interfere with the way they get along with each other. If your son understands that she is doing this for her own good and he is willing to change, then you should not interfere in the way they are getting along with each other.
If your son is not willing to change and is not happy with his daughter-in-law's behavior, but he is more reasonable, we suggest that you comfort your son in spirit. Then tell your daughter-in-law that what she did was right and good. The son did make progress, another politely told the daughter-in-law slowly, will slowly get better, I hope to help you.