and after, there is tech support

My mother is not computer-savvy, and when she's ready I'll help her sort out my father's computer stuff and (I hope) break into his account so we can sort out whatever household stuff he was managing online (like bill payments). She has "an old password" written down; here's hoping that helps.

She mentioned, in passing, that she'll contact their cell carrier to drop his line -- no sense continuing to pay for a second phone, after all.

Do I need to prevent her from doing that until we determine whether he was using 2FA for anything? I haven't figured out the right search queries that will cut through what you should do in advance lest you lose your phone. Like, I don't know where or if he was using 2FA, so I can't just go in and set alternate recovery addresses or something. The point is to be able to get into those accounts later, when my mom is ready. Does she need to keep paying for cell service so that phone number will be able to receive texts, or is there some other way to handle that? Should I go with her when she visits the cell provider (yes she was going to go to a store and do that in person)?

Anybody among my readers navigated this before?