Oh not at all, my partner has a child from previous as well and she is 10, we tend to have her at the weekend but if we do have her on a school night she is in bed for 9
i know how you feel its a nightmare for us coz i have a daughter who is 7 and she is in bed for 8 on a school night, so when the eldest comes round, we have to let our daughter stay up till 9 with the older one, may only be an hour but she is tired from that in the morning, ( having trouble with this one at the mo) or there would be trouble and arguments,
i think its different when you bring kids up together in the same house, if they were both mine, i would have the younger in bed for 8 and the older in bed for 9, thats what me and my sisters did as kids, but these to are very competitive, and your cant do anything for one and not the other, its just so different to having kids brought up in the same house, and its hard trying to control kids that are not your own!! and there is always the factor of you doing something differently but then having to bite your tounge about it lol but thats another story!!
dont worry just be strong and let them know what time is bed and make sure they start gettign ready 10 mins before
good luck xx