Boys:
Lukas Samuel-I like both names, but I think it sounds more like Luka Samuel than Lukas Samuel.

Gavin Samuel-This one is ok.

Samuel Gage-I like this one alright.

Greyson Samuel-I'd go with this one since I love Greyson.

Girls:
Mackenzie Grace-I'm not into popular names and IMO, Mackenzie is just too popular.

Gracyn Denise-I'm not in love with it, but it's ok.

Keiran Denise/Grace-IMO, Kieran is a boy name. The combos are otherwise nice.

Leigha Grace-This is a nice combo, and my choice from your girl names.