I was thinking 12% interest, and a percentage in the ownership of the deal? 

The goal was to move on to higher priced markets with better appreciation.The objector’s viewpoint: I need to own a home first before investing in real estate – build equity and experience in home ownership and then move on to investment properties.I need to invest somewhere closer, states such as Nevada, Arizona, or Texas, so that I can hop on a plane and be there in a few hours if need be.

When you have it in the company, you can leave the company to your children and then they can take over the ownership without having to pay land transfer tax etc.Your accountant is the best place to get answers on this and your estate planning lawyer can also help with questions.

Is there an option that involves terms, or something similar (much like a lease option) that would allow a buyer to pay more over time while still transferring ownership now? 

Still 100% owned by occupant - no shared equity and no changes in ownership to a new entity.

I currently am renting a house that I would really want to retire in. I can’t afford to offer what the market value is, so I’m wanting to see if they would consider me buying 50% and I would handle all responsibilitie...

There are a few work-arounds, like getting an ownership interest in the property, but those are all a bit taboo as well. 

@Nikola Magdelinic, change of ownership doesn't mean the code violations disappear.

How can I take ownership of this property while getting my grandmother the money she wants / needs to secure her for the final years of her life.

How can I take ownership of this property while getting my grandmother the money she wants / needs to secure her for the final years of her life.