My DD and I had eight years of guinea-pigs over a cycle , 8 in total , 4 males , 4 females in a rolling cycle , 2 of the boars were castrated to live with sows . At one point we had 5 , a castraed boar and his 2 wives and another sow pair who wouldn't bond ( but once we got down to the boar and one remaining sow -from the pair- they married and lived happily )
So in essence , you need to keep adding a partner or two .
My NDN kept hamsters and ended up taking in a few unwanted ones . Her lounge was full of cages 
She thought guinea-pigs were "ugly" ( I know - the cheek
)
I had never handled a hamster until I helped her catch a Houdini Hammy .
Much as we loved the piggies (and I kept them myself from 9-22yo which was why I was more than happy for my DD to have some when she was 9) they are hard work
They're untidy
They don't smel but the hay does
You cannot put them in a small animal ball rollabout , they need a lot of floorspace .
They are gentle, noisy greedy little animals , but they are not the brightest .
They are very very unlikely to bite - only if your hands smell of food , you pick them up badly or if you are taking on one with a poor history . All ours were rescues , only one would give you a gnaw , not a bite though .
You should consider rats though.
They are sociable . Their cages need to be huge but you can build upwards they are agile .
And clever .
Like all small rodents you need to read up on illnesses . Guinea-pigs do Well-to-Dead . they hide illness .
We have 2 cats now (my DH wanted some cats once we were pigless ) . They are easier in many ways but I do miss nice dry sunny days with the guinea-pigs in their outdoor runs .
With all animals their is a smell by degree .
Our piggies were cleaned daily (especially when indoors)
The hay smells more than them but it is non negotiable . Check your DS isn't allergic to hay or fur .
Males don't smell any worse than females (but they are tidier IMO) . Sows can be a bit evil in season (temper and pee) but it lasts 36 hours.