[Owner Financing/Wrap-Around Mortgage]

I can't cover the entire scope of what you need to do to successfully complete a "subject to" deal.
However, I can tell you that banks do not typically call the loans due as long as the payments continue to be made on a timely basis.
There's a lot of paperwork involved in making sure that you cover all aspects of the deed transfer and do it correctly so as to no give the bank any reason to call the loan.

You should spend the money to buy someone's course on this topic.
The course should include all the paperwork and step-by-step instructions.

Here is one course that I found.

https://www.creonline.com/catalog/c-286.html

I can't vouch for this since I have not seen the material, but it's only $97 so it's not a huge loss if it's not up to par and there's a 60-day guarantee

Best of luck with this.

[Owner Financing/Wrap-Around Mortgage]

If there's a mortgage in place, you will most likely want to do a deal "subject to" the existing mortgage.

There are many places to find the details on how to do this type of deal.
You just have to make sure that you complete all the correct paperwork.
Search for "subject to" or "sub2"

Good luck