Please refer to this guide:
Long Term Balanced General And Special Needs Guinea Pig Diets
Guinea pigs four months of age or younger should receive:
1 tablespoon of young guinea pig or alfalfa-based pellets per piggy per day
1-2 tablespoons of timothy based adult pellets
If you suspect that they are closer to six months of age, then your piglets only need one tablespoon of pellets per piggy each day.
Too many pellets can lead to unhealthy weight gain.
Please refer to this guide for hay choices:
A Comprehensive Hay Guide for Guinea Pigs (incl. providers in several countries)
I believe that oat hay is most commonly mixed in with other varieties of hay. I am unsure, though. I will tag
@Wiebke @Siikibam and
@VickiA to confirm.
Hay should consist of about 80% of your guinea pig's diet.
What exactly do you mean by Timothy Oat Hay? Timothy and Oat, to my knowledge, are two different kinds of hay. Do you mean mixed together?
You can feed sweet potato safely, but please do not feed daily. Fruits should be limited to once a week or so (as an occasional treat).
Here are some (but not all) of the veggies I give my guinea pigs:
Twice a week:
Parsley or kale
Carrot
Everyday:
Romaine lettuce
Red leaf lettuce
Cilantro
Fennel (when available)
Red bell pepper
3-4 times weekly
Cucumber (1-2 small slices each)
Once a week:
An orange slice each or a small slice of tomato
I can also recommend:
When you give your piglets veggies, shake the pellet container to create a positive/happy association with the noise.