Charlotte and Charlie are different full first names, i dont think it matters if they get called the same name (yours as a nickname) and if you dont ever see them then thats even more reason to not stress about it. I have a Briella and my cousin has a Bella, my Briella gets called Bella all the time, it didnt put me off at all (well my Briella was born first so a bit hard for me to get put off lol, but it hasnt worried me at all).