I tried really hard to read all of that, but you need to sort it out and restate it.

You told us they are Divorced, so what she made has no bearing on him if you are filing Single. Also, you didn't state if he continued to pay for family coverage the entire year, or there are month to month changes to show when he was no longer had family coverage. You mention an Advanced Payment, but is that an Advanced Payment Credit or an affordability payment? You mention mortgage interest and property taxes, which have nothing to do with the health coverage worksheet values or 1095A entries. You stated what his AGI is "now" but not what it is for purposes of the Health care coverage limits. You didn't state how this all shows for the limit of 401% of the poverty level. You want MAGI:

https://www.healthcare.gov/glossary/modified-adjusted-gross-income-magi/

And I don't understand how what she paid to BC/BS affects his tax return if they are filing Single.

Could you please sort it out and give the details that are pertinent to the issue? Thanks.