Here are my thoughts-
Silas-I really like it. I think that it fits great w/Grant. It’s simple, boyish but not too macho, simple, fairly classic & grows up well. It actually fits the best w/your girls too, because it’s maybe the most exotic of the bunch. It’s getting pretty popular if that bothers you. Not too bad, but rising up the charts.
Sutton-I personally find this completely masculine, & I really like it w/Grant, [name_f]Anya[/name_f] & [name_f]Inga[/name_f]. However, most of the world seems to think that this is better as a girl name. This may also just be a personal issue, but I have a hard time saying those 't’s in the middle of names. Like, it has to be intentional or else it comes out sounding like Sudden, you know?
Pierce-If I’m being picky, I do prefer [name_m]Piers[/name_m]. It looks sleeker & [name_u]French[/name_u]-er. [name_m]Pierce[/name_m] is the more common spelling though. It’s a very handsome name that fits in great w/the bunch.
Clark-Another good choice. Solid, handsome, short & sweet. Not too popular, but well known.
Clive-This is my favorite! It’s the most interesting from the list. I just think that it sounds dapper & also kind of cowboy-ish.
Hope this helps.