I just got married and lived with my husband's parents, grandparents, but my home was too small, so my husband and I moved out.

it's not possible to change the lock, which will intensify the conflict. discuss with your husband, and the husband will solve the in-laws problems and the wife will solve the family problems. Everything they eat in the refrigerator is a trivial matter. If it's not private, bear with it. If it's private, communicate with them. It's not a big problem. They will live together in the future and learn to accommodate. In fact, the old people care about you and understand each other when they go to your place. As long as they are not malicious to you, everything else is trivial.