Anyone with stepkids?

I love my two stepkids to death. I introduce them as my own and my husband and I have full custody. Their moms are pieces of crap. I feel exhausted trying to prove myself to them constantly. I feel like I give them more attention than my own daughter because I want to prove that it is better at my house. They make me a better person and I wouldn't change that but it's so tiring. I feel like I don't have any more to give to another child for example. 
​Mostly a vent.