They're too similar.
If the age gaps are quite close, that can often overlap them in social groups (e.g. a couple of school years apart, or same Brownie pack) and it makes it harder for them to be remembered and identified as individuals if the names are similar looking/ phonetically similar.
Years into parenting, it's easy to blurt out the wrong name anyway, either when tired or just that you've snarled at child A and that name sticks when you talk to child B. If the child has a clear identity, it's easy to shrug off, but if they already feel like they have a merged, indistinct identity, it's that little bit harder.
Colette is far too similar to Charlotte, and Chloe looks too much like a short form as it contains all the same letters in the same order.
I once had a parent on the phone who didn't know which of his 3 "A Smith" children a hospital letter was sent to as they were all under paediatrics, and he had to phone up every time to find out which child to bring. Probably not possible these days, but we ended up adding a fake initial onto the admin system to make it more distinguishable without having to phone up every time.
Nicole and the middle name is a pleasant complimentary name with enough distinction of its own.