Hi and welcome
Please be aware that the crucial chewing molars and premolars at the back of the mouth are constantly ground down by the silica in hay and fresh grass. Both the growth rate of their back teeth and digestive system (which is laid out to break down the nutritious but tough grass/hay fibre in two runs through thr gut) have developed on a mainly hay/fresh grass, which should make about 80% of the daily food intake.
The visible front teeth are self-sharpening in a balanced dental system; they are there to pick up and cut the food.
Chew toys are enrichment but they are NOT needed to keep the teeth ground down - that happens by eating unlimited hay and only a small but balanced selection of preferably green and leafy veg and fresh herbs, which replaces the wild forage with which guinea pigs will supplement their diet for minerals, vitamins and trace elements that are not present in large quantities in fresh grass or hay. What many people don't know is that fresh growing grass is actually high in vitamin C and is the reason why guinea pigs never had the need to make their own in the first place. 1/8 cup = 1 tablespoon of pellets is there to round out the diet but pellets are too soft and low in fibre to contribute to griding down teeth (they soften as soon as they are in contact with saliva), the same as a diet too high in veg.
The best chewing material and enrichment is hay and fresh growing (but dog pee free!) grass - you can offer different varieties as a special occasional treat and make them work for it. Willow, apple and pear wood is safe for guinea pigs.
Please be aware that most pet shop toys are for their owners but of no interest to piggies. They love getting their food served imaginatively and having to work for it, from unwrapping to sprinkling.
You may find the information, ideas, tips and warnings in these links here very helpful, eye opening and certainly interesting:
Enrichment Ideas for Guinea Pigs
Potentially Dangerous Cage Accessories And Toys
Long Term Balanced General And Special Needs Guinea Pig Diets
A Comprehensive Hay Guide for Guinea Pigs (incl. providers in several countries)