If you want to know if the home is an approved rental housing unit, check with local housing officials.

If you have a house sharing arrangement with your landlord and she lets her boyfriend move in, he's there with her permission.

If you have a house sharing arrangement with a smoker, and you have nothing in your agreement that forbids smoking, then you renegotiate when the lease term is over, live with the smoke or move.

It is not clear from your post if you have a mouse infestation or if you live in an area that happens to have a lot of mice running around. If it's the former you can try formally requesting extermination and, should your landlord refuse to assist, you can consider other possible remedies. In terms of cockroaches, there's no such thing as "a few cockroaches". If you see a few, there are thousands (they live where you can't see them). If this is a row house, not a detached dwelling, mice or insects may be coming from neighboring units - beyond your landlord's reach. In most places where cockroaches are a problem, the landlord will periodically exterminate the roaches. Note that if your landlord takes the position that you're responsible for the infestation she may attempt to charge you for the cost of extermination.