I used to have a separate hotbar for Selene and Eos like some of the macros above. I figured out I could just macro Selene and Eos' abilities on to one icon and it will use the one of whatever fairy is summoned. Even if the icon is for a different ability, the cooldown for the ability used will be correct. Tested it extensively before doing this. For example:

Fey Covenant and Fey Caress share an icon on my bar.
/macroicon "Fey Caress"
/pac "Fey Caress"
/pac "Fey Covenant"

When Selene is out, Fey Caress activates. When Eos is out, Fey Covenant activates. I use the caress icon because I like the color better but the cooldown timer will be correct regardless of which ability is used. Also is Eos is out in the example above, the icon will look gray like you can't use it--but the ability will still activate.

I have Fey Wind and Fey Illumination macro'd this way as well. Works nicely enough for me though it may not be what you are looking for.