Aw, I'm sorry you've had so much trouble.
My advice would be to start from scratch. Forget all your backwards steps and bad luck so far and reacquaint yourself with them all over again.
Don't pick them up just yet, unless it's absolutely necessary. If you keep 'forcing' them to be held while they're so uncomfortable with being handled, they're only going to see you as a threat. Prey animals like guinea pigs see hands coming at them like a predator's talons, and it's frightening for them until they learn to trust.
You need to be really patient. Keep trying to get them to take treats from you. Make it something they find irresistible. If they don't take it from you after a while, don't just leave it for them, take it away with you. (If you leave it, they'll learn to wait you out and get it when you're gone.) And don't use the treat to lure them out and pick them up, or they'll stop trusting you. It's to get them comfortable being close to you so that you can pick them up when they're ready.
When you do pick them up, pick them from underneath and make sure to support their back end, and hold them gently but firmly enough that they feel secure. Don't stand up and carry them about too much until they're more confident, just hold them while sitting down, calmly and quietly.
I know it's been a couple of months already and you want to be able to give them a squish and a cuddle, but stay patient, be gentle, give them time. They'll come around. Stay positive.