Visits and co-parenting?

So, I have been dating my boyfriend since October 2018 and from December through March 2019, I lived with my boyfriend at his grandparents house. I was always the one taking care of his daughter, no questions asked from day one unless he was on his off days (he works snow removal very long hours in the winter). Even though her grandparents were there she was always left with me. Then out of the blue they kicked me out. He found out after it was because his sister was running her mouth and lying about me. Prior to all this I met the baby mama once during a pick up and she had never said anything about me but now that we are getting our own place my bf would like to have visits at our house because ever time his daughter sees his phone she is asking him to call me and she always says she misses me. The grandmother is saying we can't, that the baby mama won't allow it and neither will she. But we aren't sure the baby mama has said any of this so I was just wondering how we bring it up with her so it doesn't sound accusatory or if he should bring it up on his own first and some suggestions on how to mediate the problem if she actually is concerned.

I have over a decade of babysitting experience, I have taken babysitting classes, a parenting class, i have cpr c and aed as well as first aid, I have a half dozen siblings and over a dozen nieces and nephews that I have helped raise since infancy.

So any suggestions , do we invite her over for coffee after we move in to talk or like what?

Any suggestions are appreciated because my period is late and we don't want his family to get between his children knowing each other.

Also just any general advice on how to do this step-mom(ish) thing because I have divorced parents but mine never had a healthy co-parenting relationship so I'm not really sure how to even approach this whole situation.

Thanks 😘