You're overthinking the 6-letter pattern. The baby will be an individual in her or his own right.
I could look for patterns in my parents and siblings' names. There are two I can see and mine doesn't fit it. Does it matter? No.
Pick a name you like and don't push for the letter count or you'll be choosing something because it fits (e.g. Lillie, Mollie, Jaxxon)
Your girls' names are all diminutives whereas Phoebe is more of a classic or nature name.
I'd avoid another -ie/y name or you have another pattern.
Of your names, I like Connie. Reuben fits classic and 6-letters, and Jasper fits nature (ish) and 6-letters but they're both just ok. The other boys' names are surnames and a diminutive and end in -ie.
You could choose from a huge array of names like Thomas, George, Arthur, Hannah, Joseph, Samuel, Steven, Andrew, Dennis, Gordon, Duncan, Fraser, Daniel, Dorcas, Rachel, Louise, Tamara, etc. or from something less traditional like Willow, Elliot, Maxine, Angela, Monica, Evelyn, Amanda, Pascal, Roscoe, Marina, Walter, Ronald, Jaques ...