Sub2 question

When buying a property subject-to, is the existing lender going to exercise its due-on-sale clause or qualify you as the new mortgage holder when it finds out the deed has been transferred?

Or are conducting the transaction so that the lender doesn’t find out?

In most Sub2 transactions, those are the risks involved. Has lender ever called a loan due? Yep, I’ve seen it. Do they want a property on the books if the loan is being serviced? Usually not in most markets.
There’s only one way I know of to do it safely. Look for posts on this board by MtnWizard. He details it well.