I've always said that keeping guinea pigs is more akin to keeping snakes than to keeping hamsters, as there is so much more to think about, and they really are exotic pets (and many vets charge as such); they are also about 5x the size of hamsters. The things that will sell them to your parents - well...some piggies can be as friendly as dogs. They can (and should) be let out of their cage to run around a suitably protected room (hard floor best, in case of accidents), and become part of the family in a way few small pets can. They will very quickly learn their routine, and at feeding time, or in fact, any time you open the fridge, open a plastic bag or move, they will wheek at you and come running, paws up on the cage yelling at you to feed them. They have very distinctive little characters, with some being more friendly than others. Some like a cuddle, some don't. I seldom cuddle mine, but sit in their cage, and they jump up on my knee to be hand-fed treats (I cheat and use their nuggets, and they haven't noticed the difference). If you get yours from a rescue, you should be able to judge their personalities. Piggies seldom bite (there's a section on when it might happen) None of mine have ever bitten anyone - although Groucho does like to pull at your clothes, and if you have a scooped neckline, he'll just pull your skin instead, which feels like being pricked with needles!
I have 5, and they can be quite expensive to feed in winter when you need to buy all your veggies, but in summer, I feed mine almost exclusively with grass, dandelions, strawberry leaves, fruit bush leaves etc. etc., so it is much cheaper. (Always having at least 80% hay- but hay is relatively cheap)
I've been very lucky, in that none of mine have ever been ill (touch wood) so only had a few check-ups to pay for so far.
I hope you talk them into it - why not show them some videos from YouTube of super friendly piggies (your parents aren't to know that they're not all as friendly as that. lol)
