I’m so sorry. I have a lot of random advi e about things that worked for my family. But everyone grieves very differently.
My advice is a little different to above. Both of my mum’s parents passed within 3 months of each other. My grandfather we knew was coming, my grandmother was so sudden and unexcepted that when we went to the nursing home to clean out her room one of the staff cheerfully asked how she was doing at the hospital, it was just a UTI after all. We had to be the ones to tell her that she passed, she was extremely shocked. Anyway, that’s not really the point, I just felt like sharing.
In their last moments neither grandparent was mentally present. My grandfather was unconscious/asleep for days with only soft moaning, he was in a lot of pain and we knew that the sooner he moved on, the better. I don’t know that I 100% regret seeing him like this, but I don’t think that he would like to think that my last memory of him was like this. He would much prefer that the last memory be him swearing about politics at the hospital the days before. Seeing him so helpless and lifeless was awful and I truly believe that my presence was not a help to him at that time.
My grandmother was the same, I went to visit but those last hours were awful and she also didn’t seem to know that we were there. I don’t treasure those memories at all and sometimes think I would be better off without them.
So, visit if you are still a benefit to them. If you aren’t, some times we don’t need to see our loved ones that way. But everyone is different.
As for coping with afterwards, try and talk with your FI now about what you might need from him. Obviously it’s hard to know exactly but if you feel now that you’ll need to be hugging your mother and not him at the funeral, or vice versa, say it now so that he knows the best ways to support you. A lot of people might call to see how you are, that was awful for my mother, here she was trying to get on with life and deal with the practical aftermath of both parents dieing (wills, nursing home bills, the house, bank accounts etc etc) and people kept trying to talk to her for hours on end about how she was feeling. BUT for others they would love nothing more than to talk about it with people. You don’t have to know now what you want but at least give your FI a heads up that he might need to be the one to answer the phone for a while and tell people to give you space.
Also, once it happens, take care with who you tell, what you post on social media etc in the following hours. I know many people who found out about a death through a mutual friend or Facebook, not from their families because the family was waiting to tell them later that day, in person or until after work because it was their first day at a new job etc. It doesn’t go well when people outside the family know before family does.
For the funeral, do what is right for your family, not what you think people will expect you to do. My grandparents had a good role in the community so the funeral could have included a lot of non-family. We didn’t want that. We had the ceremony at the grave site to make things simple, no flowers, simple coffin, very low fuss and very much focused on just the family. It was perfect for us and them. My grandmother would have hated the thought of us spending money on flowers that die when we could have bought clothes or jewellery. For my grandmother, we didn’t toss ash into the grave, we emptied bottles of glitter in. It was spectacular, absolutely perfect for her and made us feel very comforted.
Again, I’m so sorry. You will get through this.