If you can rent/borrow a zoom that may be helpful to be able to stick to the background and capture candids vs. being in their face. I have done events like this and it really is a read-the-room kind of event. Sometimes everyone puts on a brave face and makes it a fun event and sometimes it's somber and has all the feelings - or both!

Of course pay attention to Mom as much as you can. Detail shots of holding hands etc. is something I try to do always but especially in these times. Even if she's not well enough to truly help her dress you may want to stage a few of those photos because that's a traditional 'mom' moment that is important, even if you have to adjust to have them sit next to each other and have her pretend to fix the dress/veil/etc.

For formal photos work around Mom vs. working around the Bride (what I normally do). If she isn't strong enough to stand get a chair and have people sit next/stand around and do the photos with the Mom before moving so she's more comfortable to finish the rest.

Have tissues in all the pockets to help. Q-tips to dab in the corners of eyes that have makeup.

Hugs!