I like Nathan with your other boys names and I love Nathan Thomas as a first/middle. (I just imagined yelling them into the backyard like "Sean! Ryan! Nathan! Dinner!" I think Iain is too close.)
Yes, it's definitely too close and I think the spelling would be confusing in the states. I like Nathan and Cole. I'm leaning toward Nathan since it goes best with Thomas and is more classic like Sean and Ryan, whereas Cole is a little more modern.
I wouldn't use it if you have a Ryan already, too close. All the other runner up names are fine except Grayson. I've never liked that name. Nathan is nice and so is cole, but I like Colton nn cole more than just it by itself
Re: What do you think of this sibling set??
DD1 born 5/24/10.
Missed M/C at 14 wks Feb 2012.
DD2 born 5/14/13.
Missed M/C at 9 wks July 2015.
TTC since September 2012
TTC since September 2012
Nathan is nice and so is cole, but I like Colton nn cole more than just it by itself