West: Frank is currently Isadore's boyfriend so yes Matt will still be part of the family, as he is Matt's grandfather.
Even if he was not, Max is not dating/sleeping with a Crampton but still part of the family (or if you like, extended family).
Mark: um, no... Someone will know. Stef would know just by looking at their guilty faces. And so will Cody.
Besides, I am waiting for the next story after this one where Matt is 25 and JJ is 19 and dating some hot girl hockey player that is a better player then Matt and we get to see which brother will nail the girl first. I am betting Matt