Colton and Carson match too much IMO but it's up to you if it bothers you or not. Carsen doesn't make it better and will be more confusing for the child because that is not a common spelling.
ETA: by more confusing for the child I really mean that their name will just get misspelled all the time. So more annoying is perhaps a better word than confusing.
Re: Brother for Colton
ETA: by more confusing for the child I really mean that their name will just get misspelled all the time. So more annoying is perhaps a better word than confusing.
Landon
Zane
Jacob
Parker
Sawyer
Dustin
Rowan
Everett
Emmett
Brock
Spencer
Wesley
Carson is a good name. No big deal that they're similar.