Will it bring bad luck to our family if several people sleep in my house?

There is no such statement, but we should believe in and worship science in our present life, because our present life is based on science, so we can have a happy life now, so we must adjust our mentality at this time and don't have such an idea.

There won't be any bad luck with this. If the other person is engaged or married, this time is completely normal. For them, they are all guests, so it is completely feasible to respect them or have fun together at this time, so this is also some social relations in normal life, and I don't have to care at all.