i remember being in this position a few years ago. my bf's daughter was 14 when i met her. she was nice to me and glad that her dad was happy, but she tested me a lot once i moved in with her dad. because i had a step-dad move in with my family when i was a pre-teen who took over the house, i tried really hard not to do so. i failed though -- i kept cleaning up after her and my bf, and putting things "away" -- a concept that seemed new to the household .

She did not have a good relationship with her mother and probably would have liked if i had been able to fulfill her needs more -- she was attracted to loud confident women, and alas, i am not that. But the upside is that now, years later, we do have a good relationship, although not a close one.

I hope you enjoy the company of your bf's kids. If you can do that, i am sure you can build a good relationship with them. Best of luck!