The people that run these companies usually come from an "investment banking", real estate, or construction background.

High risk since most fail, but big rewards. 

I pay my mortgages through my banks App and there is a button I push that switches it from the monthly payment to being able to allow for a one-time principle only payment.

And does his bank accept it? 

You might want to check with local credit unions or community banks, as they’re often more flexible with second mortgages. 

The bank is going to want to know that.

Banks are getting tighter and may have unperforming assets, so they are looking at their portfolios and becoming more picky, for lack of a better word.When the economy is ripping, banks loosen criteria.

I'm guessing you probably won't be able to get a bank loan with those items missing so you might be stuck with them installing them.

If your using financing the bank requires this.

You can do a subject to transaction but that is not legally assuming the loan.the banks got rid of assumable mortgage long time ago.