I hope nobody here hates me for this post.... Like how I hate my beautiful sister in law who complains that she can't gain weight

I absolutely love my step daughters! They are 4 and 9, my husband and I got married when they were 1 and 5. We have since had two little boys together who are 1 and 2. They girls are wonderful big sisters, the boys adore them! We have 50/50 custody, I am a stay at home mom, they are in daycare on their mom's weeks (her choice to work, she is crazy loaded).

The girls love me, call me mom (their choice! The oldest asked if it was ok when we got engaged and I told her it was just a name, she could call me whatever she wanted and I would love her no matter what). They also call step dad, Dad, and feel like they have four parents who are committed to raising them and love them. And I absolutely love them, not the same as my boys, but not outwardly different. My goal in life is to never make them realize they were any different from the boys, as in step vs bio.

The problem (yes there is a problem, I'm not just bragging!!) is that I do all of the work as a mom, more even than their own mom since they are in daycare all day every day over there. I know that I did not give birth to them, that I am not their real mom. But can't I be special to them and have a good relationship in spite of the fact that I am their step mom? Does step mom have to equal nothing? I never get any of the benefit of being mom. As childish as this sounds, I want some of the perks! Out of respect to their mom, I pass on all the fun girly things they like to do so that it stays special with her. Their favorite thing is to go get pedicures, they go almost monthly with their mom (spoiled!). So I don't because that's their thing. BM still feels like I am a huge intrusion on her life and relationship with the girls, but I don't know what else to give up. I don't take them shopping, to the hair salon, nail salon, anywhere she likes to go. I've tried to find other activities that are completely opposite from her to foster my relationship with them, camping, hiking, bike riding, parks. But it's hard some times to do all of the hard work and not get the fun stuff. I do 90% of the parenting at our house, I wipe their butts, do the laundry, cooking, etc, but God forbid I get to take them school supply shopping, that would be overstepping my boundaries!

Are there any step moms out there that have survived in the long run? I feel so fortunate that I have the kids I have, they are so sweet to me and truly are a part of our family unit, but man it can be so wearing!!! How do you parent them as if they are your own without getting hurt when you are reminded that they are not? I want so badly to do right by these kids, and I work very hard. But I'm worried that I will end up resentful towards them and their dad for the situation, and for always pushing my feelings aside.