Horse People Out There

Riding close dependsss on the horses. Tom would school them to accept another horse that close. In the Spanish Riding School in Vienna the stallions perform in close formations, often the riders are knee to knee, and the stallions are nose to tail, probably the most threatening position.This takes many years of training with one dedicated rider who rides the stallion for his performance lifetime.
As far as females (mares) with males, most of the males are castrated (geldings) and they can coexist for the most part. Again it can depend on the individual horses, though.
I think the biggest safety concern is riding pell-mell over feral ground - rabbit holes can result in a snapped leg, a broken shoulder or neck for the horse; the person riding could be maimed or even killed. That could also be your concern about riding knee to knee, but most people who ride horses know and accept the dangers in exchange for the incredible high you get when you both move as one with such power and grace.
even killed on the fall.

Please ignore the last line, it was an editing holdover that I thought was deleted. My S key apparently sticks too.
Cheers.

You're bizarre,friend.