The mortgage doc states that if the property is sold or transferred "without the lender's written consent, the lender may require immediate payment in full of all sums secured by this Security Instrument."

My experience with Waterstone is that they sell the mortgage off to another bank quickly within 1 year, and their underwriting was extremely strict which led me to provide A LOT of documents and having multiple 3 way calls so they can get information from various sources that would require my consent. 

Verify that the 1st is current from the holder, if it's current without issues the chance of the second being clean is much better as well.I see you're a lender, since I had a pending credit transaction pending I could run a credit check on the makers, consent not required so long as the holder had consent

You might as well record the conversation while you're at it, Wisconsin is a one-party consent state so you can legally do that.If the next contact doesn't go well then I would go ahead and file for eviction and let them know it is being processed and will move forward unless they pay rent immediately.

I'm guessing its not legal to lock him out without his consent, being that he is still currently on the lease. but I'm not a lawyer.

I'm guessing they sublet to the meth dealer without your consent, so you probably had recourse to evict them at that point.  

(I sure already have their consent signature).Thank you!

My 30k LOC through RBC was closed (without my knowledge or consent) because in Jan, I paid off the balance in full when my house was refinanced.

The factors to be considered would include consent, time and materiality. 

The contract states "I'm not allowed to rent the property without his written consent during the contract period" I guess I thought screening renters would be okay.