USA here. If you were trying to use these names for brothers, yes. Much too close.
[name_f][/name_f]But [name_m]Stellan[/name_m] is fine on its own. I have a pretty nominal Midwest “non” accent though.
[name_f][/name_f]A few other similar sounding names:
[name_f][/name_f][name_m]Sterling[/name_m]
[name_f][/name_f][name_m]Stefan[/name_m]
[name_f][/name_f][name_m]Stratton[/name_m]
(no St but still in the ballpark imo):
[name_f][/name_f][name_m]Sebastian[/name_m]
[name_f][/name_f][name_m]Silas[/name_m]
[name_f][/name_f][name_m]Simon[/name_m]
[name_f][/name_f][name_f]Skylar[/name_f]