Hand-feeding works with most pigs. Pigs
love food. Try to learn what their favorite veggies are. Offer it to them several times a day. They might not take it from you at first; you have to be patient. Just leave your hand in the cage with the veggie or fruit and out of curiosity they'll come up to you, even if it's just to sniff what you're holding. They'll eventually take it from you and they'll soon realize you're the Food Person. Food= Good. Human With Food= Good.
Another tip is to give your pigs some laptime. You can do both at the same time, or separately, depending on how comfortable they are on your lap. I give Flyn, my tamest pig, 30-60 minutes of laptime daily. I try to do it at the same time each day. Bramley, on the other hand, hates being touched and picked up, so I leave him be. Some pigs will really look forward to snuggling on your lap, while others might not.
Honestly, not all pigs will become tame. It takes time and patience. Some pigs are just more shy or more skittish than others. Some pigs will never like being touched or picked up. There are pigs like that. You have to accept them for who they are. Guinea pigs have different personalities and it's important for you to know what your pig does and does not like.
It can take a month to tame your pig, or even several years. Getting them when they're young can sometimes help. Younger guinea pigs seem to be more daring. I got Flyn when he was around 8 weeks old. Because of his outgoing and adventurous personality he warmed up to me in no time. He was even the first pig that gave me piggie kisses during laptime
How long it'll take to tame a guinea pig really depends on their personality and how patient you are. Don't yell at them or get mad when they don't run up to you for food or squeak at you for attention. Give them time and space if needed. Sometimes the best way to tame a big is to just give them their space. You wouldn't really like it if somebody kept bugging you, would you?
Good luck! Don't get discouraged if they don't become tame soon!