Advice - I love my stepchildren but hate being a stepmom

I've been with my boyfriend for a little over 3 years now. He has 2 children from a previous relationship, F-11 and M-4. The M took to me right away, maybe because he was so young but the F took a bit longer but we're close now. I absolutely adore them and love them as my own and would do anything for them.

But its a painful reality realizing that you're really nothing to them when it comes to BioMom. Everything she says goes. And since the M has gotten older he likes to say things, well my mommy does this or that, or my mommy let's me do this or that. His dad as already said to him not to say that and that what we say goes in our house.

I don't disrespect or talk negative about their mom in front of them, I voice my issues with her directly to their dad when it's just me and him. I try to sound happy when her name is mentioned. I grew up in the same situation with a negative stepmother so it's has always been my intention coming into their lives to be good and happy and let them know they're loved, which they are.

Its just painful being a stepmon knowing that they don't see you or respect you as a second mother to them. They don't need to call me mom/mommy. Although the youngest did for along time until one day he "suddenly" started calling me by my first name, which isn't exactly an easy name to say and my bf calls me a nickname or baby most of the time which makes me think it was biomom and biograndma teaching him to say my name, the "oh she's not mommy, she's. ...." thing. The F-11 is very well behaved and listens when I ask her to do something, but the youngest I feel is more moldable to dislike me because he's younger and van be taught to.

I just need to advice or words of wisdom to keep me positive.