Any advice on keeping so many family members away?

These semi annual visits are undoubtedly not a picnic to bro and family either with the expense, giving up their vacation time and the stress of travelling with kids (and their inevitable whining that they would rather stay home with their friends), maintaining the family connection must be very important to him. And since they are travelling a great distance it's not like they can just pop in for a short visit, they want to make the trip worthwhile. I would think long and hard about whether the inconvenience is really worth totally ending this kind of family connection. And remember that some people like to fuss and grumble about all the negatives but secretly enjoy the event.

Given that the OP posted in the summer I assume the visit has already occurred - I wonder if any of the fears about germs were justified?

Unless your father has some mental issues, this is really his issue to discuss with your brother. I would not get involved in the discussion.

I can't imagine how I would receive "don't bother bringing your germ ridden children to visit me." Probably not well.

Sometimes in families issues can't be avoided. If brother responds bad, I'd try to ignore it and let it roll off my back. If family members can't put dad's needs first, they have issues that they need to deal with.

Since, your dad at 95 has told you his concerns and what he doesn't like, I'd have no issue being his advocate and as pleasantly as I could. I might first visit with dad's doctor and bring up the flu, colds, loud noises, etc. and how it's wise to take precautions. The doctor would certainly agree on limiting access to illness and anything that stresses dad. So, with the doctor's sanctioned advice, I'd notify family members that after discussion with dad's doctor the following will happen. And then say whatever you feel is appropriate.

It's quite common for children and loud noises to bother seniors. So, limiting their visite to one-half hour, shouldn't be a problem, PLUS, they all wash hands and wear masks. Adults too.

I might also explore having them stay elsewhere and rent a room for family gathering. That way, dad can leave when he's inclined.

Also, can they change visit to avoid cold/flu season? Even if you get the flu shot, it can really take a toll on a senior. I had it last year, even with the shot and I don't think a senior would have survived it. And, I'm pretty sure that I got it from my young niece. I didn't know she had the flu when I was cuddling and playing with her.

Since you live there, it is your home. You may not own it, like you don't own an rental, but it is your home. The hotel is a good idea. I think they should pay for it. Is there some way to get fewer people visiting at a time? You say 6-8 people with two being children so this is 6 adults? Why do they all have to come at the same time? Can you think of some excuse to limit the number of people at a time. Maybe you can say dad can't spend quality time with individuals when there are so many people at once. There is absolutely no way I would be able to tolerate 6-8 visitors in my home and I'm middle aged. If I was visiting someone and they wanted to set some type of limits, I would be glad that they told me. Clearly there is a problem with your brother, if he can't hear about any limit to his behavior. I suggest you, and maybe your dad as well, go to see a psychologist for a few sessions to learn how to set boundaries. This was very helpful for me.

could your dad offer to pay for the hotel (**if money isn't an issue) and act like it was a gift from him - maybe they would like having their own space and they wouldn't be as insulted.

Do these people stay with you? My cousin got around this when sister was bring 2 adults and 5 children with her. There was one guestroom. He informed his sister that the septic system would not handle all those people so they needed to find Hotel rooms.

Hand sanitizer and face masks all around

I had an uncle who as he grew older found the normal noise of childhood really "got on his nerves" - even the grandchildren he dearly loved. He loved their visits - but loved seeing them outside much more than in the house. So the house rules were the kids were only allowed in the general portion of the house for about an hour at a time during and just after meals. Other times they needed to play on the porch or in the yard or watch tv/movies in the bedroom set aside for their use. Kids were told when you get old sometimes its just harder to cope with a lot of people and noise and they needed to help Grandpa by being quieter and playing outside. I don't ever remember this being a problem (although my aunt probably explained this need to her sons) - I guess we just assumed that an old man had a right to ask for reasonable considerations in his own home.

Are there similar accommodations your family members could make during this visit? Would it be possible for the younger family (grands and great-grands?) to stay at a nearby hotel and visit 2-3 hours a day? Maybe visit in the morning and join for dinner each evening?