First of all, I'm really sorry to hear about your grandmother
That must be so hard for you and your family, but hopefully you can find solace in knowing she's at peace.
Regarding weight loss, the old truism still exists: if you think you can't, you can't. You definitely will not lose weight if you have convinced yourself it's not possible.
I'm a very literal/logical person so whenever I run into the same thoughts you have, I remind myself that weight loss is simple: if I consume fewer calories than I burn, I will lose weight. It is in fact possible, I remind myself, to lose weight, I just have to eat less and move more. It comes down to biology, and that's objective.
I know that weight loss has a lot of other elements to it than this simplified version: there are lots of emotional, physical, and psychological issues at play when trying to lose weight. I don't want to try to claim it's easy. But again, for me and my very literal/rational self, reminding myself "This is scientifically possible, you just have to commit and make the right decisions." helps a LOT in getting me back on track when I try to convince myself it's not possible.
You can do this, it's about making one decision at a time, one day at a time. Focus on the smaller things than about Weight Loss as one huge mountain you have to climb. When I need help I look at goal posts or even mini goal posts. There are so many people who have done this, there's no reason why I can't!
We are all here to support and cheer you on!! You can totally do this!!