I don't really know anyone else in the same situation as we were in, but my parents seperated when I was about 3 and my brother was 1. We stayed with my mother until I was about 5 but she was ill and struggling to cope and left us with my father and new stepmother. We saw my mother a couple of times a year but things were really volatile between them all and we were put in the middle and used as ammunition a lot. When I was about 5 or 6 we were told that I had to call my SM "mum". I haven't thought too much about it but have been having some counselling recently which has got me reassessing some things.
For one thing, people have always found it very confusing knowing which person I was referring to when I said mum. But more recently it's struck me as almost Orwellian - I think my father and SM have literally tried to remove any trace of her from history. I got a serious earful recently (am in my early 30's it's ridiculous!) because someone had been persistently commenting on a fairly striking physical difference between me and my SM and I eventually said, well, it's not that weird as she's my SM, not my biological mother. I was accused of denouncing my family and rejecting them, which I thought was a bit much, it's a biological fact that half my DNA is from my mother!
It's not as if I can really revert to calling my SM by her name, (even though they have totally ostracised me recently for having contact with my biological mother)but I guess I'm just looking to see if it's fairly normal for step families to work in this way, or if it's another example of mine being controlling?