You need to explain the dynamics of these calls to your Mom because she's not getting it. We went through this with our parents, too, but now they get it.
Adults don't need to do FaceTime to stay in touch and, to be honest, a lot of us don't like it. I find awkward to be on camera for extended periods and it's uncomfortable to have to stay in one room or location while talking to my parents on the phone. I prefer to keep in touch with them via phone calls and text, which have worked perfectly fine for many years. I don't personally get more out of seeing them on camera and I don't actually enjoy it that much either. But we're all adults who can converse on a phone and read and write texts and emails, so this makes sense for us.
FaceTime is pretty great for little kids who can't do those things. We do FaceTimes with our kid and her grandparents, and it's a good opportunity for her to get to know them, share things about her life, and get some face to face interactions with family who live far away. Sometimes they read stories to her, sometimes she shows them her toys or something she made. It's nice. The calls are not long, about 15 minutes, as that's the right length for her. The focus is on her because she's the one who needs it.
When my parents/ILs have been demanding about making this "full family" calls, here's what happens: instead of talking to our DD, they talk directly to us, mostly about things that DD cannot sustain interest in. They want to talk about someone they know who died, their health problems, stuff going on with house repairs, neighborhood gossip, etc. DD can't listen to this stuff. She wanders off or, worst case scenario, gets frustrated and starts trying to get us to get off the phone. These conversations can go on for 30-40 minutes because they have a lot to say. DD can't do that. She's 4. It doesn't work.
Also, while some of that is okay for the DIL or SIL in the room, I don't personally think my DH needs to listen to my parents discuss their health problems for close to an hour. I will absolutely do it, they are my parents. And my DH wants to hear how they are doing and cares about what's going on. But he doesn't need the whole thing. And vice versa. My MIL always wants to talk about people in her town who I've never heard of. I can definitely have those conversations with her but not every week for an hour! DH can do it because he actually knows those people and the conversations have relevance to him, but to me it's just random gossip about strangers.
So we do FaceTime with our DD and the focus is on DD and both parents do NOT need to be there because it's not for us. We each talk to our parents on the phone regularly and keep in touch via text, and then our parents can talk for as long as they need to about whatever they need to discuss, and they can get into sad or difficult subjects and not worry about boring DD or us needing to deal with her (our spouse can focus on DD if we are home during these calls, one of the nice things about having a spouse!). And we can also each stay in touch with our ILs with shorter phone calls and texts, which makes sense for the nature of these relationships.
I don't know where my parents got this idea in the first place that a sit down FaceTime with our entire family would make sense -- people got a lot of weird ideas during Covid about how stuff is supposed to work. But it doesn't! Just explain this to your parents, especially your mom, and let them know that this is how other families do it, too. Trust me, everyone is not sitting down to a weekly FaceTime with their ILs every week, and if they are, it's likely they have different family dynamics (not necessarily better). This is how your family works, do what makes sense for you.