Okay-first , I love guinea-pigs. DD and I share ours, I kept piggies when I was 9yo through to early 20s.
So, I'm not going to tell you all the good things about guineas, I'm going to tell you the bad. Are you ready for this........... (Sounds like Watch With Mother, Are you sitting comfortably ?)
They are vunerable prey animals. They need to be protected against predators (cats,foxes,birds -magpies, hovering birds of prey, dogs,rats, badgers)
Cold, draughts, damp, heat
So outside they need secure, clean, dry,draught free housing.
Inside they need to be protected from any other pets, smaller children, noises,fumes,draughts,heat.
They are messy, dear Lord the hay. They need hay to survive , but my stair carpet has a hefty share of it. The hay smells worse than the pigs if they're clean.
They are respiratory vunerable to dust and fumes which is why sawdust and shavings aren't adviced.
My guineas have their hayboxes cleaned every day in Summer, every 2 days in winter if I layer the bedding (so clean paper,soft straw hay one night. Fresh paper and hay on top the night, then starts again) They pee so much they'd be swimming after two days.
Mine have a wooden playhouse to live in and rabbit runs+ outdoor house for summer when we're here to watch them.
I'm in the SE but I can't leave mine in the Pighouse all winter, its too cold and damp overnight.
They are noisy which is quite charming with their squeaking and they'll let you know if you're late with their breakfast. Like horses their digestive system relies on pretty constant throughput , hay, pellets, veg, grass.
Also like horses they cannot vomit so if anything goes in that shouldn't.....
And they eat their droppings but they're very distreet with it, they eat the first passing then they pooh the second time , guinea pooh is the most inoffensive animal pooh.
You need 2 or 2+ so you'd need to work out if you want 2 boars, 2 sows or 2+sows, or a neutered boar+sows.
There's no guarentee that they'll get on. Boars can squabble, sows can squabble.
They need more space than you'd imagine especially with boars. The Minimum of 4'x2' for 2 adults is really tight.
They are very lazy little animals , some will cope with ramps (like in those double storey hutches). Some don't.
You need to look into what they have to eat (hay, the pellets , they need Vit C which is in the food) and what they cannot eat.
You will need to check their weight,teeth,claws,skin,fur,ears,eyes.
Make yourself aware of the illnesses they can have.
Don't ever assume your DC will do the care (my DD is flipping excellant but I know sometimes she's busy or jiggered so I do the PigCare). we had 5 until recently, now 3. Two are hers, one is mine.
You will end up in a spiral of pigs when one dies and you have a singleton.
And - when they die , they break your heart. You'll feel guilty that you missed something (they hide illness) or you have to make the painful decision to PTS.
You'll need to find a Guinea-Pig Vet . You might never need one , but know where they are.
So that's the Bad&Ugly 
The Good far outweighs.