There are some flowers that Guineas eat, things like roses, pansies, echinacea, nasturtiums would be ideal, they would be piggy safe.
I would probably cut down on the amount of cut flowers just in case though, especially with strong smelling flowers like jonquil daffodils (I think they smell awful anyway) or potted plants like hyacinths, saying that these would both be best avoided as they're both toxic for Guineas (most flowers/plants from bulbs are).
I personally wouldn't have lilies in the house at all with any animals, as I was reading the other day about a cat that didn't come into direct contact with the lilies/pollen, but the vet still thinks that was the cause of its death
Humans can also be sensitive to the pollen. (the smell of them also makes me want to urge, so I'm not sure Guineas would like the smell of them either!)
I'm sure the occasional bouquet of flowers would generally be ok tho, as lots of Guinea owners keep them as pets indoors & probably have bunches of flowers as gifts.
Just be cautious that the plants can't be eaten, wherever they're positioned.
Xx