It would depend on how relaxed your homely cats are with other cats on their territory. Some are laid back, some will fight to move the outsider away from their territory and some homely cats are homely because they aren't happy about meeting outsiders out and about due to nerves and that could cause serious health problems with your home cats when they have an outsider living in close proximity.
The feral may not take kindly to having 'outsiders' in its territory and start bullying any cat coming out of the house or staring them out through windows

If you take one check you can have say a month trial to assess your own cats behaviour . That way you will notice any stress behaviour, urinating in unwanted places or bladder blocking and risking kidney function.
Cats are loners by nature and have large territories. All I can say is you don't know until you try it but beware of possible problems developing.
Also consider using a feliway plugin at home, and if possible also where the feral will stay, for a few months to minimise the likelihood of stress and severity of its effects.
All that said, It would be lovely if you could give a feral a lovely home. They don't do well in confinement at Catteries and aren't rehomeable as pets. And added bonus of resident rodent patroller
