I like any of those with Jack and Alexa. None of them sound like a totally different style of name.
Honestly, I'd just pick my favorite and not worry about having a matching set of names, because once they are grown it won't matter whether their siblings' names sounded good together.
My favorites from your list are Benjamin, Andrew, and Ryan.
Re: Fill in the blank...
all of them except Hunter.
i like ethan and benjamin the best.
Ethan, Andrew, or Ryan
I like any of those with Jack and Alexa. None of them sound like a totally different style of name.
Honestly, I'd just pick my favorite and not worry about having a matching set of names, because once they are grown it won't matter whether their siblings' names sounded good together.
My favorites from your list are Benjamin, Andrew, and Ryan.