Hi and welcome
Please try to find a vet who is confident with operating on guinea pigs - a good vet is key to operation success! Guinea pigs sadly have and still don't feature much in a general vet's curriculum in many countries, so knowledge and operation skills with small furries can vary enormously.
You should find the information in this guide here helpful and interesting. Only one of your pair needs to be neutered. It is generally boars, as most vets find neutering easier than a more invasive spaying operation, but there are some dissenting voices.
Please be aware that there has to be a 6 weeks post-op wait with boars. The little surprise baby in my avatar is the last gift from a supposedly over 5 weeks post-op boar (not one of mine, I hasten to add).
The guide does contain links to recommended vets in several countries. Perhaps you have one of them within your reach?
Neutered / De-sexed Boars And Neutering Operations: Myths And Facts
My very first own guinea pig was a neutered boar back in the 80ies, who was still going strong when he died aged 6.
I've always had neutered boars when I came back to keeping guinea pigs. I currently have got 9 boars; 8 of them are neutered and the 9th will be as soon as he reaches the minimal weight my vet is happy with for operating.
I have and have had several spayed sows; the oldest was 5 years when she was spayed and am currently saving up for another spaying operation for an ovarian cyst sometime next year before it can go wrong.
PS: What has happened to the babies? Please be aware that you need to separate any baby boars from mother and sisters at 3 weeks of age or you are facing the next round of pregnancies with an even higher risk of fatality than the usual 1 in every 5 births going wrong even with the best of care. It is one of the main reasons why we are a strictly non-breeding forum.