With regard specifically to the mortgage interest limitation, the federal appellate court ruled in Voss vs Commissioner that unmarried co-owners are each entitled to the full limitation. In other words, the mortgage interest limitation applies per taxpayer, not per residence. The IRS subsequently agreed to abide by this decision.
https://law.justia.com/cases/federal/appellate-courts/ca9/12-73257/12-73257-2015-08-07.html
Similarly, the SALT limitation applies per tax return. Thus unmarried co-owners each benefit from the full $10K limit.
Remember that each taxpayer may only deduct the amount of mortgage interest or property tax that they actually paid.
Your question about the home energy credit is answered under "Joint occupancy" on page 3 of the instructions for Form 5695:
https://www.irs.gov/pub/irs-pdf/i5695.pdf#page=3
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
