Need Advice: Biomom is resistant to hiring tutors for kids

Hi all,

My partner and I desperately need advice about how to help his two children (16M and 12F) succeed in school. Since around the end of last school year, both kids have needed a lot of help with their schoolwork. For context, their custody agreement is ~60/40 with their mother as the primary custodial parent (she receives child support), but functionally the kids spend almost exactly 50/50 at each house. SS (16M) has a great work ethic, prioritizes schoolwork, and spends a lot of time studying independently. This school year, he has entered into some more difficult classes (i.e., math) and has needed a lot of extra assistance with homework/studying at home to grasp the material. SD (12F, diagnosed ADHD) struggles to get started and remain focused on homework tasks. Often, even talking about homework has led to explosive emotional responses from SD. We have created a system where I normally tutor SS (I have more of a math background academically) while my partner tutors SD. This has improved SD's ability to complete homework and study while at our house, but this is not reinforced at all at Biomom's house. The explosive responses from SD often result in huge fights with Biomom that ultimately end in SD not completing any (or very little) schoolwork when she's at her mom's house. After weekends at her mom's house, SD is already starting the week extremely behind in her classes. My partner and I both spend hours each week working with both kids to keep them afloat in school.

To deal with the lack of schoolwork at Biomom's house, we have suggested that both kids have tutors. Biomom has been extremely resistant to this. She says that "their grades are fine and they don't need tutors" (they both have low Bs in classes), that it is "too expensive for them both to go weekly" (we have offered to pay fully for all tutoring sessions), and that "she doesn't want to drive them" (the tutors could come to the house or the kids could be tutored at school before their sports practices). We could hire a tutor on our time so we have more free time, but the real issue is that the coursework is not reinforced on their mom's time. I am also worried that if my partner or I have a particularly busy work week and can't spend hours helping them, their grades will slip dramatically.

We have tried to foster good independent schoolwork habits with SD based around what works best for kids with ADHD. We started SD in therapy to work through some of these big emotions surrounding school. We have looked into small study groups after school. We drive them to school early for short 'office hour' sessions with teachers. I even suggested to my partner that he picks the kids up, takes them to a cafe, works with them for 1-2 hours on her weekends. Discussions between my partner and Biomom to try to get her to help more and/or help organize tutoring sessions happen almost every other day. These conversations started at the beginning of the school year. Do we just set up the tutoring sessions on her time? I feel like that's overstepping. Do we hire a tutor on our time to cancel out some of the time that we personally spend working on schoolwork with them? We are completely lost. This sounds ridiculous, but do we just give up on trying to coordinate this and just let the kids struggle? Any advice or insight would be helpful! Thank you in advance!