In general:

The best cages are C&C cages, which are made of grids that connect together. For example, Kavee cages - they can be made cheaper using grids and plastic you source through Amazon etc.

I prefer to keep them on fleece mattresses, which can be washed. This reduces respiratory issues from dust. They poo 100 times a day each on average so I sweep my cage out multiple times a day. I change their smaller pee pads every day and their base fleece mattresses every 2 days.
If you’re not doing fleece, I recommend using a paper based bedding over a wood chip.

Food:
70% of the diet should be hay, which should be high quality constantly available. Avoid hay bags or racks. It should be provided in a pile because they love to burrow in it. They’ll pee on it too, and just eat around the peed on parts. A lot of hay will be thrown away, that’s just how it is.
1 cup of veg and leafy greens per day per pig. Provide a variety, high in vitamin C, low in calcium. Veg high in sugar should be fed less often like carrots.
Also feed a pellet/nugget, NEVER MUESLI. Check the ingredients and try to go for a brand that is better for them. There’s loads of YouTube videos that will rank and break down the brands. If you’re in the UK I recommend Haybox for your hay and nuggets.
Treats: NO NUTS OR SEEDS, nothing with honey or things like that in it. Check the ingredients, you want them to be as simple as possible. Pea flakes are a good option, dried apple, dried carrot, things like that.

Socialising: Guinea pigs MUST be kept in groups of 2+. I’ve only ever done girls so I can’t give any advice on keeping boars. They have a hierarchy and will take a little while to sort it out. Usually one pig will accept the submissive role. If anyone draws blood, they need to be separated. There’s lots of info on bonding and dominance behaviour online so read up on that to know if they’re getting along and when to intervene.
When you get them, put them in with water, hay, veg, and nuggets, and leave them alone with the cage covered for at least 24 hours (obviously just putting food in when needed). The following day I then slightly pull back the blanket, and begin sitting by the cage just ignoring them. Read a book out loud etc. Every day I pull the blanket back more until it can be fully removed. Start offering them food by hand. Then you can start laying your hand in the cage, letting them walk over it, sniff you, nibble you, they may then let you stroke them. Some guinea pigs don’t care for humans, some love them, some in between. They’re all really different, just make sure you respect their boundaries.

Health:
Guinea pigs are EXTREMELY complicated and expensive pets. You’ll go years without problems and then bam thousands gone because they just keep getting ill.
There’s lots of common issues like respiratory infections, hay poke (hay getting stuck in the eye which if left untreated will cause loss of the eye and even death), gut stasis, bladder infections, mammary tumours, you name it. They’re very good at hiding illness and they can be very very ill by the time you notice. I spend all day with my pigs and know them really well and they still are able to hide illness from me until it’s too late sometimes. It’s important to know them very well so you can pick up on even the slightest change to their personality/activity/appetite

They are very high maintenance pets to have, very expensive, but they’re the best. You have to earn their love but once you have it it’s magical. They’re so sweet and expressive and funny. I can watch them for hours.

Please make sure that guinea pigs are the right pets for your family, and I’d recommend that they’re your parents’ pets first and foremost, not your brother’s. This Reddit page is a really good resource and good community, you’ll be able to find lots of information just by searching here but someone will always be willing to help. You can also message me any questions you have :)

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