@Stumpy2
As I said, you do not have to be listed on the mortgage to deduct mortgage interest, as long you actually pay some of the interest and are either a legal (on the deed) or "beneficial" owner.
2. This will be my second home, but only for a month or two.
A second home is any home that you own, that you decide to call a second home, even if you don't live there. You just can't have more than one second home for the interest deduction. If you mean, it will become your main home because you plan to move in, that's fine too.
does that create a problem with capital gains or any other issues?
The sale of your current main home is completely separate from any other purchases or transactions. The rule that you could postpone capital gains by purchasing a replacement home was eliminated in 1997. The current rule is that you can exclude the first $250,000 of gain from your taxable income (or $500,000 if married filing jointly), as long as you owned that home for at least 2 years and occupied it as your main home for at least 2 of the 5 years prior to the sale. See publication 523.
https://www.irs.gov/forms-pubs/about-publication-523
I feel like the safest thing is just to be on the loan.
That's more of a legal matter between you and your son, and not really a tax matter. Every co-borrower is jointly and severally liable for the entire loan amount. That would mean, for example, that if your son fell on hard times and stopped paying, you are responsible for the entire amount even though you only live in half the home. On the other hand, being listed on the mortgage may give you more rights and more advanced warning if something bad did happen. But you shouldn't decide that based only on the tax treatment.
