You can neuter him and keep him with his family or you could get him a friend. If you are getting him a friend I would try to find one about his age and get him as soon as you can. If they are introduced when they are both young, there is a bit less chance of trouble. If you are waiting to get a friend then you'll need a different aged boar (younger when your current boar is an adult). Or you could get him an older boar to be friends with him. Or you could even keep him on his own near the girls (where he can still smell, see, and talk to them just not reach them) and he will be just as happy. There are pluses and minuses to all of the options but he will be happy with any of them. What it boils down to is what is best for you and your situation. Can you comfortably house another piggy, especially if things don' work between them? Does neutering make you too nervous? Do you have room for another cage near the girls to house him alone? I personally would keep him alone near my girls. Any type of surgery makes me nervous and when it's not for a health concern, I'd rather not. I also get nervous about boars fighting. I tried to introduce a pair of mine who always got along ok during floor time but when they were put together they had a big bloody war the first time I left them alone and one ended up with his tummy ripped open. I know that it doesn't always happen that way but it makes me nervous now. So keeping him in his own cage near the ladies would be best for me. That may not be best for you though. I have 7 boars and 8 sows. All my boars live seperated except Bastian and Kiba who insist on being together. One of my sows also lives on her own because she is a rotten little bully who constantly harrassed her cagemates. They all live in the same room though and talk back and forth to each other all the time. Alot of my friends have neutered boars in with sows and/or unneutered boars buddied up. All the piggies in all 3 situations are happy and spoiled. The best idea would probably be to sit down and list out the good things and bad things about each living arrangement and then use the chart to help you decide. It's often easier when you see things all written down, at least it is for me.
Now about what the vet said.....
Check them again several times as they grow up until you are sure. If you have a piggy friend near by, maybe you can get them to help you if you aren't confident in your opinion and see if they agree with you. Or maybe, if you can, take them back to the vet for a "re-sexing" a few times.
Are you saying the vet said to live him with his mom and sisters until he is 8 weeks old? If so, I'm afraid I would ignore that advice. Baby boars have been known to impregnate sows at as early as 3 weeks old. It's rare but it is possible. 8 weeks is definantly too long to stay with mom. Most breeders reccommend seperating at 3 to 4 weeks. Some seperate at 3 weeks if the boar is mounting his cagemates and rumbling around after them otherwise they leave them until 4 weeks. Other seperate at 3 weeks unless the boar is very small and having trouble growing then he will stay with mom a bit longer. They tend to look very lonely in the big cage all by themselves at that age, I know, but I've found if you give them a big cuddly stuffy to curl up with they settle in quite well.
-kkat
You would just have to take into consideration if they didn't get along, would you have space to separate them? Good luck with whatever you decide.
Yes, I think it would be best to get a baby boar from a rescue