Hi!
Guinea pigs regulate their body temperature vie the blood flow through their ears. That is why ears should be hairless and why there should be a bald patch (symmetrical on both sides) behind the ears to allow optimal ventilation.
These guide links here (which are part of our very useful New Owners guide collection) will help you to learn what is normal or not and how to monitor their health with a life-long weekly body check and weigh-in:
Guinea pig body quirks - What is normal and what not?
Weight - Monitoring and Management
Boar Care: Bits, Bums & Baths (as you are not mentioning the gender of your piggies)
Here is the link for our full New Owners guide collection, which you may want to bookmark, browse, read and re-read at need. It also features a chapter on settling in and making friends with your piggies by understanding how their prey animal instincts work and how to 'piggy whisper' by using their own socially interactive key gestures to make them feel welcome and loved instead of waiting until they figure out us humans:
Getting Started - New Owners' Most Helpful Guides