(Been away looking after human family, the pigs have been abley cared for by DD)
We had GP3 originally (when he was bereaved) and got our GP4 and GP5 to side-by-side while he was neutered and went sterile.
We did the whole Neutral Ground (paddling pool) with a big Salad wedding Cake and baths to formally introduce them.
Our sows were feisty Rescues, both more than equipped to take on GP3.
When he died , the girls had each other for 3 months until we got GP6 because there was just something missing (A Lardy Boar).
They ate, peed,poohed,were cuddled, but didn't utilise all their space, just seemed to hang out in the haybox.
GP6 came ready neutered (2 weeks post op) so after 4 weeks he joined the sows (bath, neytral ground etc)
Unfortunately, our newest girls (GP7 and GP8) haven't joined the Herd but I think it's the very strong characters of GP4 and GP7 (two large tri colours) who don't gel.
So GP6 has his wives (they live as a trio) and his ladies in waiting (as a duo) side-by-side.
Boars are lovely and snuggly and he'll love the company of the sows. (It's the sows that are more of a challenge 
)
Neutering does carry risk of course but do check that your vet is experienced in small animal castration (they'll neuter more rabbits than guineas) , have a check up done to make sure he's physically fit and he can wave his 'bits' goodbye and prepare for his new life.
He can side-by-side until he's sterile then he'll be very familiar with the sows when they meet.
Our boy Bert highly recommends married life (he was a brother:brother pair but they fought and were seperated)