Yes,barmy 4 boars is very usefull website.
I have in the past had gruops of as many as 5 boars together.I currently have 3 together who are very happy,no scrapping at all.I have also from time to time had pairs of boars. It all depends on the personality of the boys,laid back boars will mix happily,stroppy,or highly sexed boars are a problem,and usually have to be housed by themselves.