Heat can be very dangerous to rabbits. Sitting out in a hutch can be miserable on its on, but it’s doubly miserable when the rabbit is dealing with summer heat and humidity.
It’s not just wild animals that can harm or scare a rabbit outside, domestic dogs can certainly do that, if one is running loose. Then there are parasites to deal with – fleas, ticks, and the very dangerous flies.
If a run isn’t fenced in on all sides, including the top and bottom, then predators such as hawks or any animal can get in or the rabbit can dig out.
Rabbits are much happier and safer inside.
Regarding getting a friend for your rabbits and housing them together. Rabbits have to be spayed and neutered, with a wait period of at least a month after surgery before they can be introduced to another rabbit. It doesn’t matter what gender they are or if they are litter mates. They must be spayed and neutered, then go through proper bonding procedures, which can take weeks or months or not work out at all, which means the rabbits cannot be kept together.