Those two are fairly similar in my book; X is such a distinctive letter that using it in both kids' names feels like overkill to me. What about:
Dashiell nn Dash
Griffin nn Fin
Shea or Shay
Sullivan nn Sully, Lee, or Van
Truman nn Tru
Garrett nn Rhett or Barrett nn Bear or Rhett
Declan nn Dex (gets your hint of X in there!)
With just reading the title I immediately thought Paxton. I have not heard of Paxson.
I'm going to beg to differ... I love having the x as a theme in each child's name. I'm not too big on Paxson, but Paxton's ok... What about Alexander, Xavier, Knox, Xander, Hendrix, Dexter, Felix, Fox, Rex, Maxwell, Maximilian, Xerxes, Xavien, Lennox, Huxley, Dixon, Phoenix, Saxon, Braxton, Axel, Essex, Fairfax, Xan, Oxford, Saxton, Halifax, Onyx...