I like
Iris almost enough to consider it.
Ines doesn't happen where I live, so no.
Irene sounds good to me with three syllables, but since it always seems to have two, it could only be a mn for me.
One out of three does not a sibset make.
Iris,
Ingrid and
Isobel could work, or
Iris,
Imogen and
Isobel. Or, to get three different I- sounds,
Iris, Irmela and
Isobel. More interesting that way.