It used to be that you had to have Indefinite Leave to Remain for Help to Buy. You might want to check into that before you get too far down the rabbit hole.
Where do I start trying to find that out?
When I opened my HTB ISA in 2016 (just before my husband and I found our house!), there was nothing in the application that asked if I had ILR. I had to submit identity documents to verify my eligibility for the account and nobody cared. I read the government scheme's website about it and nothing there precluded me from getting it...
Since I had only just opened my account when we found our house, I didn't have enough to collect a bonus, so my HTB ISA still exists. Apparently, spouses can have separate ones, and as long as
you've never had interest in property, even if your spouse has, you are still eligible for HTB. So I've been drawing all that sweet-sweet promotional interest, and some day if something catastrophic happens, I might be able to collect a few hundred pounds from the UK government to buy a new house with.