Oh dear poor you! You don't say how old your pigs are, but if they are little and you haven't had them very long they might just be frightened and if your daughter shouts or cries out when she holds them when they nip her, she will unfortunately unwittingly make matters worse. Do you pick your piggies up and then put them on your daughters lap for cuddles? Some pigs nibble as a way of tasting/testing things when they are little, almost their way of learning what they can and can't bite!
The other possible problem could be that they have mites (which you won't be able to see) and their little bodies are sore and this is their way of telling you holding them hurts them. Have you seen much scratching going on and do they have any obvious hair loss? Mites are easily treated, but you will need to visit your vet who will probably apply some Ivomec topically - both piggies will need treating.
Assuming mites isn't the problem, try offering food to your piggy without picking them up initially - get your daughter to do the same - offer some green beans or a long slice of carrot, something you can hold one end of, keeping your fingers out of their reach. Gradually use one finger to gently stroke the top of their heads. When you do pick them up try to do it swiftly and hold them gently but firmly, try putting them on a towel on your lap. The name of the game is patience and perseverance, stick at it. If they do nibble you could try just quietly but firmly saying "no", showing that it is unacceptable to bite, not much more you can do.
Good luck with your piggies and welcome to the forum.