I would love to know a few examples of (1) approximately how much hay you give your pigs and (2) how frequently you refresh it (e.g., small amounts 3x per day, one big pile daily, etc). I have read widely about the care of guinea pigs and understand they should never be out of fresh timothy hay for their primary food source. Each day I find this is hard to balance because my pigs love fresh hay. I do not want them to run out so I give generous amounts and refresh throughout the day. However, if I give too much, they don't finish it, it dries out, and then they refuse to eat it. Dried hay also seems to become stiff and sharp and I worry about them poking their feet or eyes on it. I have three guinea pigs: 2 females and one male, all about 3 years old (rescues).
When we had guinea pigs we gave them an unlimited amount. For us, this meant having two hay bags (for three pigs) that were filled basically every other day. If it got on the floor they usually didn't want it so I think it's important to "serve" it in a bag/rack etc so it stays fresh and pee free.
Not sure what the "advertising" (I'm not affiliated with them, just a happy customer) rules are here but we used dustfreehay.co.uk and got the soft type. It doesn't dry out and isn't sharp, but the UK Timothy was so I'd avoid that.
I don't know what you meant by "fresh hay". I thought you meant freshly-cut grass from the garden or farm. I thought that would be unsustainable, unless you have a lot of field. I'm not a native speaker. I personally don't find hay go unfresh so quickly. I change the hay every two or three days. But if I have more choosy piggies I will have to change the hay more frequently. Maybe change the brand of the hay would be helpful.