I became a step kid to a 30 year old when I was 12, it wasn't easy for anyone really! MInd you when both families were there we numbered 10 so there were bound to be difficulties... I didn't mind my step mother but there were tensions between her and my mum, and her and my little sister, and of course my loyalties lay with my family. It can be so complicated as there are so many dynamics in play with step families, never mind when you add teenage girls to the mix! Don't put all the pressure on yourself to make things work, it's up to everyone to help, and if they're unwilling then there's not a lot you can do.