If we are married filing separately, can spouse claim mortgage interest if not on mortgage loan but is on the deed?

Yes, if the other spouse is on the deed, and owns the property that is listed on the mortgage, they can deduct the interest that they paid.

Thank you very much.  Would it matter if it was paid from my separate bank account rather then a joint account?

No. Basically, you can split the mortgage interest expenses any way you want as long as they aren't being deducted twice.

Thank you.

You're welcome!