here are some more!
Hi and welcome
Your two boys are both looking well within the normal variation for American (USA)/short-haired smooth (UK) piggies to me.
The shine on larger boy looks within the normal healthy range to me; it is more visible on darker piggies.
Satin piggies lack the dark shaft inside their hair so their hair is lot shinier than this. You can see comparison pictures in the chapter on satin guinea pigs in our common pet breeds guide:
What-breed-are-my-guinea-pigs? Picture-guide-to-common-pet-breeds
I would recommend that you double-check both their gender and feel the smaller one around the ribcage whether he is a good weight for his size (checking the heft or BMI) - the normal weight variation is much larger than widely suggested. Weight charts are frankly not worth it - by artificial mathematical definition, half of all piggies would be declared as outside of the average weight range even though there is nothing wrong with them and they can live to a grand old age just the same as 'average' piggies. 'Average' is entirely arbitrary human concept.
A once-weekly weigh-in on your normal kitchen scales is one of your most important health monitoring tools but you need to know first whether your boys are at the upper or lower end of a healthy weight span at their current size so you can interpret any grow and changes (especially loss) appropriately and put any weight loss into the correct context.
More practical how-to advice on various aspects here:
New Guinea Pig Problems: Sexing & Pregnancy; URI, Ringworm & Parasites; Vet Checks & Customer Rights
Illustrated Sexing Guide
Weight - Monitoring and Management
How To Pick Up And Weigh Your Guinea Pigs Safely (videos)
I would also recommend that you sprinkle feed the 1 tablespoon of pellets (2 until ca. 4 months) per piggy per day and their veg around the cage and do not serve in bowls. This minimises food bullying and encourages natural foraging behaviour. Make sure that access to hay cannot be blocked (ideally you have it in two places in the cage) because unlimited hay should make over three quarters of what a piggy eats in a day. The same goes for water bottles - ideally one at each end so access cannot be physically blocked. Also make sure that any houses etc. have all two exits and that the boys can get away from each other if they want to.
Babies can range from ca. 40-120g on birth - the largest can be triple the size of the smallest even within the same litter; this tends to carry on throughout their life and the size differences will become even larger. As long as each piggy is a good weight for their personal size, there is nothing wrong with them and they can all live a healthy normal life span or even a bit beyond. Don't overfeed because it is still another year before they reach adulthood so each boy has plenty of time to reach their genetically determined optimal weight in good normal care. It's the quality that makes the difference, not the quantity.
At this young age you do not have to worry about overweight; any extra is converted into growth.
A good mainly hay based long term diet is key to a healthier and longer life and can add 1-2 years to a normal life-span; what can never control are medical issues that can crop up. Please save up for a vet fund as part of their weekly/monthly maintenance cost.
Long Term Balanced General And Special Needs Guinea Pig Diets
You may want to bookmark the link to our very helpful practical New Owners practical advice and information collection where you can find all the guide links in this post and many more:
Getting Started - Essential Information for New Owners