You can do whatever you want here, but your readers are going to constantly get them mixed up, especially the ones with double l in the middle.
If you pay attention, you will notice that experienced authors almost always try hard to give every important character a name that starts with a different letter of the alphabet. It's better not even to have both Gillian and Cillian. Readers continually have to pause and figure out who is doing what, and probably they will stop reading because aaargh, that is so annoying.
When I accidentally added a Carissa to a series that already had a Cassandra, I immediately gave Carissa the nickname Riss. This was not a spontaneous decision that I liked the name “Riss,” I assure you. It was because giving important characters names that look alike on the page is a terrible idea.
There are 26 letters in the alphabet. I strongly suggest you put them to use.
Someday, if you have four children, you can give them those four names. Lookalike names are far less annoying in real life than in fiction.