As to minyan outdoors, how far can people be away from eachother and still be part of a minyan?
People davening outside in an open place can join together in a minyan if the ten people can hear the chazzan and they can see each other. Additionally, when davening outside, they should be careful that there shouldn’t be any excrement or other item that we are not allowed to daven next to, because that can be considered a hefsek between the people.
Minchas Yitzchok 2-44, Rivivos Ephrayim 1-45 who says this from a number of poskim. See Minchas Yitzchok that they should also be careful that a path should not be running between the people.