DH,
Normal Mortgage loans are ALWAYS interest first, with balance to principal, figured monthly.
I’ve NEVER heard of a loan that re-ams only ONCE a year.
That’s insane.

HELOCS are usually figured on daily balances.

The “best source of a direct answer” is rarely the lender.
They often don’t know their azz from their elbow, and only confuse people with incorrect information.
(Even calling the IRS helpline results in wrong tax info)

Talk to someone who breathes this stuff, and you’ll get answers.