"Friends are friends, business is [something] aside" can I change here the business for money.
There are noting wrong to play against friends, but some people don't know how to deal with defeat. If your friend are like this, you don't have to play with him, or sooner or later you will be break you friendship.
I could say more things related to the topic, suggest other things, but this is personal and will depend on the relationship that each one has with friends, I have no friends who play poker, if I were to play I would prefer to play with fictional chips, and leave money only for private tournament and not for cashgame.