Stick to a set time every week, no exceptions. We've done Sunday calls for over two years by making it non-negotiable. Share the login details ahead of time and have a backup plan if tech fails. Skip once and it's hard to restart, so don't let it slide.
Wait, you guys actually share login details ahead of time? That's wild to me because I can't believe how organized you have to be just to talk to family. My family would never stick to a set time every week without fail. We tried it once and my uncle forgot his password every single time. It became a whole thing just to get him online. How do you deal with people who are just bad with tech?