Hi PeachMelba, and congratulations on your pregnancy (yes, yours too!)
I know you said you wanted to hear from people in your position, and not biological mothers, but as I'm here and my dp isn't, I'm just going to express my sympathies. My dp went through exactly the same and I know it was very painful for her. And continued to be, exacerbated by being a different racial origin from our dd, so everybody always asks if she's the nanny.
It is REALLY painful, and you will probably go through lots more of the same, and I'm so sorry for that.
Sorry to heap on more bad news, but I noticed you saying you are both going to have a mummy role. Quite right, but one thing that has happened with all the lesbian parents I know is that they expected to occupy the same role in relation to their child, and were really shocked when the child didn't accept that. Most times, the biological mother - who was breastfeeding and usually on longer maternity leave - became intensely close to the child and the non-biological mother felt very left out.
This may be easier if you have twins, I don't know. And I'm not telling you to freak you out, because the good news is this: it's absolutely natural for children to want their parents to occupy different roles, not have two identikit parents. I DON'T mean gender roles - I'm not suggesting you play daddy - but understand that your children will want you to bring different things to the relationship, and will play you off against each other, and at various times may be quite rejecting to one of you.
In our case - and I think this is quite a common pattern - our dd definitely preferred me when she was a baby. It was tough for my dp, but she persevered and gradually built a very special relationship with our dd, quite distinct from how I act out being mum (they are very physically close, and talk all the time, and play brilliant games together - I am project-manager-and-grazed-knees mummy). Right now I am definitely the third wheel in the relationship: our dd REALLY prefers being with her non-biological mother. And that's ok, because I know she loves me too, and right now she just needs more of what her other mother has to give her.
I wish we'd known 4 years ago how this would work out, then I think it would have been easier for us both - and particularly my dp - to feel calm and positive about our unfolding relationships as a family. Babies are programmed to love their parents, and yours will love you. That will bring you such joy, and be a huge consolation for the shit and nonsense we all have to put up with from the outside world.