I used several methods to get my 6 piggies used to us - 1 of which however is still slightly nervous - all my piggies ive had from babies, so i'm not sure if this makes the bonding process easier.
Because guinea pigs love food i always associated lap time with something good and always grabbed a bit of their favourite food. It did take some time before they would take it from me, but i did this everytime i petted them or handled them.
Another thing i always do is talk to them. When they were younger, i used to sit next to their cages and just talk to them, eventually they would come out whilst i was sitting there. I also kept any sudden movements to a minimum. Again i used the method of holding a piece of their favourite food to coax them into coming near me.
I would also try and get them used to being handled by getting them out for lap time a couple of times each day - but by keeping it short and sweet (say 5-10mins).
Do you have an indoor run or area they could run around in? When i got my first piggie, i found this the quickest way of him getting used to us and his surroundings. We used to let him smell a small piece of his favourite food in our hand then call him to the side of the run - once he knew we had yummy food, he was racing everywhere.
3 of my 6 guinea pigs will stand there and allow you to pick them up - however the other 3 require a bit of chase - so what i normally do is wait until they are lying in their snuggle bed and lift the whole thing out - this make it less traumatic for both me and them.
I guess it's just trial and error - but i'm sure it wont take long before you see the results. As i said in the beginning of my post, one of my male piggies is still skittish and he's around 9months old (and ive had him since he was 5wks old) - it's just his personality - so we do what we can to ensure he's not frightened (we talk to him quietly and approach his cage slowly) - sometimes he'll just stand there and allow you to pet him - other times he'll run - he's very much a pig's pig and i think he much prefers his cagemate's attention than ours - not at all like his cagemate who isn't afraid of anything and loves to come and say good morning.
Whatever you do, i'm sure they'll soon come out of their shell's and their little personalities will shine through - be careful though - i started out with only 1 and i now have 6 and have to stop myself from reading the rehoming section
