Hello, I saw this and thought I might be able to offer advice.
We have 4 sows, 2 pet shop (bonded) 1 from a rescue and 1 that was about to be put up for adoption. Our rescue one hates being touched but will come and get food. In saying that, she has learnt to trust my daughter, but its taken a year and a lot of work. We've accepted that she doesn't like human affection and thats OK. 3 out of 4 of mine like to take their food in private and eat in a hidey somewhere.
A guinea pig vibrating can be a sign of being content or not being happy. When you stroke their heads, do they flick you off? If not, the vibrating could be a sign of being content.
Could you have them inside for floor time? We have big cardboard tubes on the floor etc and that's when our rescue one becomes adventurous and explores with confidence.
Ours live in the kitchen and are quite used to noise, but the moment I move with a tea towel, they still run for cover (maybe think it's swopping bird!)
One thing we found useful for picking them up was picking them up inside a tube or a hidey. It was much less distressing for them.
Ours have taken up so much time, but it's been worth it. Yours are obviously adults now so you might not ever be able to pick them up with ease, but I'm sure with time they'll become used to you more. 🙂