Problems with husbands ex during quarantine..

My step kids have been here since March 23rd. We have full custody and mom has visitation. We discussed keeping them from her house this weekend due to the fact her and her boyfriend are still working and we are working from home. She at first agreed, then made it into a HUGE deal accusing us of actually going to work 🙄 when our work places have been closed. Last night she was speaking to my step daughter, we made her a painting for her bday tomorrow and her mom said “don’t rush finishing it as this virus probably won’t leave until at least August” and then stated she turned my step sons room into a room for her other daughter that lives with her. To me this makes it sound like she isn’t planning on seeing the kids for quite a while? We were planning on letting them go back over next month as we can’t legally keep them from her unless she agrees and the kids do, which they did for this weekend. We’re trying to minimize contact as it’s been nothing but her starting fights and not having civil conversations. I’m just so confused.