[Jennicat]

First of all, these sound like normal guinea pig behaviors. Part of your problem is that you're terrified that they'll bite you. You have to stop being so afraid of them. Guinea pigs very rarely bite, and usually when they do it out of extreme fear, because they're in pain, or accidental in the case of breaking up a fight.

I think it's extremely cruel that you would give away a guinea pig to the SPCA because it's not as tame as you want it to be. They are naturally skittish animals, and some that I've had for YEARS are still very scared of me, and will only rarely come out and grab vegetables. Removing her also takes away your youngest pig's friend, and it's not kind to keep them alone, they're herd animals, and they like to have a friend.

Please be patient and stop being afraid of your guinea pig. They are very gentle creatures who are not prone to biting.