Having a stepdaughter who scares me made me relate to your post.
We were married for exactly 9 months when my husbands two kids, 13 and 14, (girl and boy)came to live with us. Very intimidating.
Among our friends who have remarried, it's generally been the girls who have a difficult time accepting the new woman in their father's lives.
My hat's off to you for raising two teenaged step-children. We had some friends who, soon after marrying, had
three young teenagers (his children) move in with them. They made life a nightmare for their stepmother for quite a while. In fact they gave their dad quite a struggle, too. Their mother let them get away with anything and everything. Their dad had rules and expected them to obey them ..... of course, the kids pushed things to the limit.
For several years they went back and forth, a few months at a time, between their two parents. They would resent the rules their father imposed ..... but when they went back to their mother, they found that they didn't really like having such free reign.
Ultimately they all chose to live with their father and his wife .... and ended up being really great kids who grew into very responsible young adults ... who now adore their stepmother. But it was tough for quite a while. The fact that the father and stepmother stuck to their guns and didn't let the kids run wild is what eventually paid off .... and gained not only the kids' love but their respect. Hang in there!