My DH said he read they’d prefer to be with 3-4 female pigs
They might be happier but you'd need to have one boar in each group (and a neutered boar is quite happy with one wife) so you'd need two large cages to accomodate .
Sows can be just as feisty and stroppy as boars though !
Our forst two pigs (brothers) liked their own space we could tell they slept in different corners of the hay bed by the pooh nests . They hay box was in their shed , DH made it from an old cupboard , about 3'x3' floorspace sleeping area , open front to let them escape . We filled to the brim with hay and they just piled in. It is insulating but needs to be dry , fresh, replaced regularly (they like to sleep/eat/pee in hay )
When we got a piglet boar for GP1 (GP2 died) we gave the older boar a wicker hedgehog house with straw on top and a rubber trug cut to to over , so he had insulation and his own space ( piglet liked the haybed)
They really fretted if they were seperated even briefly but still beaved like the other one was Arch Enemy 
Last year I had three oldies , I kept them indoors 24/7 from about early Oct , mainly to keep an eye on them. They had the small bedroom (no door on it) in two big cages .
This morning I woke up to my NDN scraping ice , my first thought was "guinea-pigs" but we haven't had pigs since April when our last old lady died .
WRT veg, you do need to moderate , the darker the green (so spinach, kale Cavelo Nero, watercress, cabbage, herbs ) the higher risk of calcium build up in the bladder and kidney .
They do appreciate if you go out with the scissors to cut them grass, rinse it , dry and let it come to room temperature . My NDNs were used to seeing me out in my dressing gown with a bowl (lowering the tone)