I feed them twice a days. No it wasn't like that when I got him, must been a fight.That looks like it might be an old cut in the ear - ie not actively bleeding. It can occur if there has been a scuffle. Was it like that when you got him? Do see a vet if you are concerned
If you are feeding them unlimited amounts of hay and that hay makes up the majority of their diet (80% per day, so adding large piles of it every day), one cup of veg per day (and not feeding fruit or sugary veg items such as carrots any more than once per week) and one tablespoon of pellets per day along with giving them plenty of exercise out of their cage, then it is unlikely they will become overweight.
Ensure you weigh them both weekly so you can ensure they grow well; and check their heft (piggy BMI - you want to be able to feel a nice fat layer over the ribs but still be able to feel the ribs - the guide explains)
Weight - Monitoring and Management
Long Term Balanced General And Special Needs Guinea Pig Diets