Sister Act

What can I say about my sisters? Are they a thorn in the side, like blisters? Or my oldest friends, indeed, Always mentors in time of need, The family ties that bind, Ever ready to say "Never mind", We look alike, but think apart, Oldest friends from times long past, "Older ladies', we've ripened, Can't buy sisters with a stipend, Are sisters thorns in the sides like blisters? No, you cannot buy my sisters!