Good luck to you family Razz.
If it's part of a well supported and ongoing procedure I'm sure the benefits will far outweigh the detriments.
Obviously with all the advice they have been given, your Mum and Nan know what to expect and how their eating patterns will also change afterwards. As long as they are aware of these and accept them, you will probably find that this time next year they are feeling better than they have for over a decade.
Any operation necessitating general anaesthetic is not without risk, but this is now well established surgery and the risk is obviously deemed far less than the risk of allowing their current situation to continue.
Personally, I'd like to try a gastric balloon rather than a band, but I don't think either would work well for me. So I'm just doing it the old fashioned way
Then again, I'm only 36, I don't have diabetes and I'm not yet in a condition where I can't exercise, so I know this is the best thing for me.
You and they will be in my thoughts. Keep us updated.