Hi and welcome
Firstly it's lovely to hear that your relationship is going so well. Allowing everyone to experience their authentic selves is a priority in polyamory but each relationship usually has boundaries somewhere.
For me it's that I always want my partner to live with me. I don't mind if someone else joins us but if he wanted to start house-hopping that would be a deal-breaker for me. Luckily for me we've talked about it and he has no problem with that.
Your problem is that you didn't put a boundary around this before getting comfy in the relationship. At this stage communication is the key I think. Talk about your fears in terms of time
availability, discuss it with her husband. See what comes out of it but remember love might be abundant but time isn't, you might have to make some hard choices before getting more entrenched.