Hi and welcome!
I assume that you and your sister have got two boars that are several months old and at their hormonal teenage stage? Sadly, once there are bloody fights, they will never go back together again. Many boars are sadly bought for looks and not with an eye for whether they actually get along.
You and your parents could consider the following options:
- have the boars living alongside each other in two large cages (2x4 ft minimal recommendation) with interaction through the bars for mutual stimulation. They will calm down eventually, but it may take some time after a serious fight like yours.
- find each boar a character compatible friend by dating them under expert supervision at one of our recommended rescues, which goes a long way to stabilise a boar bond. This means that you come home with a new friend only if there has been success and that you have the rescue to fall back on in case there are problems later on.
- have both boys neutered (their fight shows that they are now old enough for it), so they can live after full 6 weeks post op wait with a sow each. Cross gender bonds are the most stable of them all and fall-outs are virtually unknown. But your parents need to find a good general vet with either lots of experience in guinea pig neutering or a small animals expert in order to minimise the risk of costly and heart-breaking complications. I have a surprise baby from a supposedly safe over 5 weeks post op boar living with me (not one of mine), so it can really happen that late. Unfortunately, neutering will not make your two boys go back together, unlike with rabbits.
In the latter two cases, the two groups can live on top of each other if space is an issue.
http://www.theguineapigforum.co.uk/pages/guinea-pig-rescue-locator/
http://www.theguineapigforum.co.uk/pages/guinea-pig-vet-locator/
If your parents would like more information, they are welcome to join the forum to help all of you find the best solution for your individual circumstances. it would help us greatly if you could tell us which country you are in; we have members from all over the world and our advice can differ greatly depending on what is available where they are.