OK - you need to be a bit clearer. Stamp duty will arise on a second hand property where the purchaser is not a first time buyer. Stamp duty may also arise on a new property if the property is over 125sq m and the purchasers are not owner occupiers. Stamp duty does not arise on a new property under 125 sq m if the purchasers are ftbs or owner occupiers.
Deal with partner first:
1. First house - ftb.
2. 2nd house - he may have been deemed to be a ftb but this depends on the terms of his divorce. Or it was a new house and he was an owner occupier.
However, the whole point about ftb relief is that it is to give ftb's a leg up - it is not to be used by investors and there may well be a clawback due if the house, as you say, was rented out.
Your house
New ? or second hand? This makes a difference. Your o.h. is most definitely not now a ftb but he could be an owner occupier. If this house was second hand and you are both on the title, then stamp duty was payable. And interest is running. If the house was new and under 125 sq m , then no stamp duty was payable.
I'm intrigued - given the number of properties your o.h. has bought ( he is on his third now) - that there should be any difficulties in working out whether stamp duty was payable.
mf