Did you try and pet them while they were eating their food, or while you were feeding them? This can make a big difference!
I've only had my two for a few months, but the things that worked (and are still working) for me were that when I started off just offering them food, I held it by just the tips of my fingers, keeping my hand as small as possible (and therefore contact between me and them to a minimal). When they were comfortable with that, I drew further and further away when offering them food so that they had to come to me for the food and initiate contact. When they were happy with that, I started putting food on the palm of my hand so that they had to touch my hand/get even closer to me in order to get it. When both were happy with that, that's when I started stroking them (really slow and light touches) and just gradually extending the time. Arthur, my more skittish guinea pig weirdly, is absolutely fine with me patting him now, and Merlin is getting more confident with it. If they move away and break contact at any point, I stop and back off. I only ever do it on their terms.
Also! What's their favourite food? Mine are meh with veggies as treats (they have them daily, but it's not what they obsess over). They, however, love, love, love, go crazy and will do anything for Harringtons pellets, so these are what I always use. I just have to move close to the bag and they come running and wheeking.