My Brother Has A Weird Rash Or Idk What It Is?

my brother has a weird rash or idk what it is we thought it was a spider but but its spreading can spider bits spread? it was first 1 red bump on hes belly now there is a ton iin like 20 minutes he got them all over hes arm then in a few hours the became on hes leg and the next day they went away and now there back alot more on hes arm face belly back legs? we seen alot of people at a haunted house maybe they had somthing but awhile we had a party with alot of people but none of my other me my mom/dad/brothers or sister or anyone that comes over is geting it he laid on the floor a couple times and he never ate chineas food and when he ate them a few days later he got then but idk if that could be it they look like Miskito bites bit there are no Miskito's around here this season its turning winter we live in indiana and its only lie 40 degrees do you know what it could be if it was a spider bite i think it would have 2 bumps beside eachother i heard not sure but he doesn't but he did have 2 bites right beside eachother on hes knees that was hes first bite then the all spread so it could be that and they all itch he said do you know what it could be? and should he go see a doctor lmfao :D????
@TVR Im A Guy XDD lmfao