No, layer feed is not good for them. Layer has a higher amount of calcium in it for laying hens. Too much calcium is hard on the males' kidneys.
No way would I have just two Guineas especially not housed with chickens. And I don't say that because I'm so addicted to Guineas, its from experience and years of raising them. If you go back and start reading you will find multitudes of posts where Guineas were pounding on chickens.
Take some time, do some reading and learn about them and their requirements. It could save you a ton of headaches and heartaches in the long term.