Hi and welcome!
Good that you are doing your research beforehand!
Guinea pigs are territorial prey animals that live in groups and prefer their firm surroundings. They are ground roaming animals and need large cages to run around in, which are not quite cheap (minimum 2x4 ft, for boars we recommend 2x5 ft). So much toing and froing can be very stressful for them.
Healthy piggies live about 5-7 years on average. Can you be sure that you will be together for so long?
They are also likely going to need vet care, which can quickly climb into the hundreds of dollars or pounds. Saving up for an emergency vet fund right from the beginning is very important as guinea pigs can go downhill very quickly and any vet treatment has to be paid upfront. This is even more important when you are still minors and depending on your parents.
I would strongly recommend to rather think about having them when you are living together and are earning your own money, so big rows over medical cost etc. are not something that can cause disagreements between you as well as a major family rift and lots of distress.
If you really want pets now and your parents are OK with it, I would recommed to rather stick to solitary hamsters or saving up for future pets for when the conditions are right.
Are Guinea Pigs For Me? - A Guide