Living at the in-laws' house is normal in some areas or countries. This is usually caused by the young couple's insufficient income to rent or buy a house, while your partner's parents are kind enough to offer their house to live in together. So, if the condition is like that, of cource it does not mean a criminal act. However, if you live at parents-in-law's house, you have to know yourself by behaving well, taking care of the house, sharing household burdens, and sometimes you need to give something (gift) to them as your thanks.