Hi
Three boars meeting each other could go well if they are all very laid back/older or it could end up in an all out fighting ball within a few minutes. Or anything in between. There is just no guarantee as to what happens. With a 6 months teenage boar looking for a new home in the mix I do however struggle somewhat to envisage the best case scenario - that is ringing rather an alarm bell. But you could consider a living alongside option if you end up with a pair and a single in whichever way.
Boars are indeed the great losers and I appreciate your wish to help them all. But they do also come with their own social wiring and quirks, which breeding practice and pet settings are cutting very much across. Unfortunately, as much as I would love to help as many boars finding companionship and a caring home, it is not a matter of simply telling you what you want to hear but a matter of what your chances are likely going to be and what precautions you need to take. There are unfortunately no 'magic wand' measures to bring about the best case scenario.
Whenever you bring new piggies home for bonding, you always need to have a plan B or even a plan C at the ready - I have had several piggies where I had to go as far as plan D or even E. With my dumped ex-single Beryn I got about as far as plan H but I did eventually find her a friend who had the will and patience to work through her massive fear-aggression issue with her.
If I there is one one lesson I have learned from adopting plenty of often stuck in rescue piggies (or potential companions for them) over the last nearly 20 years then it is the fact that you can never predict the outcome but that the cases where it doesn't work out what looks ideal on paper clearly outweigh the successful oddball bondings in my own pretty ample experience with probably coming up to 200 bonding attempts by not.
You
can have a big heart (I certainly have done it!) but only as long as you plan ahead and can always accommodate the worst case scenario and be able to think out of the box. Otherwise you can all too easily end up with a mess that is going to upset you much worse than a disappointing forum feedback - we do see those kind of messes on here fairly regularly to help nd sort them out.
PS: I have writting an article series about guinea pig social wiring and what survives of it in our pet piggies, which you may find very interesting to understand where your boars are coming from. The last chapter deals with boars. Here is the link:
The Herd, the Group and I: Investigating Guinea Pig Identity and Society