Can't give specific "how to" legal advice but see comments below.
It's easy to convey ownership from the two of you as tenants in common to the two of you as joint tenants with right of survivorship. It does need to be changed because the interest of a tenant in common has to be probated. Joint tenancy does not. You should be able to find the deed format by googling.
First of all, selling property on a land contract is very dangerous. I've read hundreds of sob stories on the internet when the deal falls through, the buyer defaults and destroys the property on the way out. Don't do it. Don't even think about doing it. Sell the property outright to somebody who can qualify for a mortgage, or pay cash, and can take title when the money is paid.
If you will your sole and separate property to your spouse it has to be probated. To avoid probate on it, use a beneficiary (transfer on death) deed per Indiana's Transfer on Death Property Act:
https://law.justia.com/codes/indiana...17/chapter-14/
Again, you can probably find the format on the internet but it's probably best to involve an estate planning attorney to help you with these property issues.

