Oh dear, such complicated little characters. I wish I could make my four intone happy herd but it's not going to happen. I went to Pets at Home over Christmas and saw a gorgeous lone piggy sow called Galaxy up for adoption. I actually enquired about her but chickened out in case I couldn't integrate her into either of my pairings, as I have two closely bonded pairs. I do wish they would all get along, but then it's their differences in personalities that make them so charming.
Good luck, I do hope you find a good solution for all of them xx