Hi megs!
I had enough trouble choosing two boys names- I can understand why choosing a fourth would be hard.
I think Tyler goes well with your boys names.

Other suggestions off the top of my head:

Kieran
Sylas
Leon
Rowan
Harry
Fraser
Morgan
Byron
Sebastian
Oran
Talan
Ryan
Miles
Finn

good luck- and congratulations on your 4th precious son.