Well, instead of Nathaniel what about Nathan or Nate? Or instead of Daniel what about Dan or Danny? What about... Henry, Jack, Mick, Aaron, Noah, Eli, Louie, Alec, Silas, Wyatt, or Neil?
I really like Iris and Lila for a girl. How do you feel about, Alice? Or Ann? Claire? Maggie? Mae? Wendy? Rose? Ruby? Lilly? Violet? Louise? Viola? Finley? Lucy?
Those are the first names that came to mind. Good luck!!
Charlie, Sam and Daniel fit perfectly imo. Daniel really isn't all that formal at all, imo at least.
What about David, James, Jack, John?
I like John with Charlie and Sam. If you really wanted a nn you could call him Jay or Jack.
I immediately thought of Henry. I also like the suggestions of Leo and Jack.
For girls, Molly, Rose, Kate, Nell, and Tess all come to mind.
Charlie and Sam are fine as they are, don't worry about giving them Charles or Samuel. I do like Samuel but I find Charles too old man, like Prince Charles.
For boys, you might like Alex, Jack, Toby, Rory, Luke, Jake, Liam, Harry or Adam.
For girls, I don't think it really matters if you use a longer name.
I'm assuming you in live in the USA? As in the UK where I am nickname-names are more commonly used than formal names. I know and have heard of loads of Charlie's and Sam's but know only a couple of Charles' and Samuel's. I think you need to take a 'British' view on this and ditch the whole worry of feeling boxed in by your son's names not being the formal choices. Don't dwell on this fact! It's common you're in Britain and every other boy is called Sam and Charlie ; )
Charlie, Sam, and Alex - it works yet I think Alex almost feels forced onto the sibling set. I'm more of Alexander fan compared to just 'Alex' as a stand alone name.
Charlie, Sam, and Nathaniel - I think Nathaniel is too long for Charlie and Sam. A gorgeous choice. Just doesn't work. Nathan maybe?
Charlie, Sam, and Daniel - It works yes Daniel is the formal choice but I think because their all short, simple names; the sibling set works!
Charlie, Sam, and Archie
Charlie, Sam, and Alfie
Charlie, Sam, and Max
Charlie, Sam, and Leo
Charlie, Sam, and Harry
Charlie, Sam, and Henry
Charlie, Sam, and Ben
Charlie, Sam, and Milo
Charlie, Sam, and Jack
Charlie, Sam, and Liam
Charlie, Sam, and Jake
Charlie, Sam, and Isla - I think Isla feels to 'modern, unique, exotic' for Charlie and Sam which are rather simple choices.
Charlie, Sam, and Iris - It works Iris is a cute timely vintage name and works effortlessly with Charlie and Sam. Three brilliant vintage choices.
Charlie, Sam, and Elisabeth - Ellie works in this sibling set whereas Elisabeth just feels far to formal.
Charlie, Sam, and Lila - She works with Charlie and Sam, Lila has a lot of spunk and seems to mirror Charlie and Sam really fashionably. I think combinations is great.
Charlie, Sam, and Harriet - I think Harriet despite her formality works effortlessly in this combination just because Harriet has this really British upper-crust aura. She seems to go with Charlie and Sam because their also popular British baby names. The theme of Britain runs through this sibling set perfectly. I think Harriet works so well. I also love Hattie.
Charlie, Sam, and Millie
Charlie, Sam, and Daisy
Charlie, Sam, and Alice
Charlie, Sam, and Beatrix
Charlie, Sam, and Ella
Charlie, Sam, and Anna
Charlie, Sam, and Evie
Charlie, Sam, and Molly (not a fan but this name may appeal to you and is super popular in the UK)
Charlie, Sam, and Amelia
Charlie, Sam, and Mia
Charlie, Sam, and Effie
Hope this helped x
I like Will, Jack, Max and Ben with Charlie and Sam. I think that if it's another boy, you should go with another nickname name so that they all go together. Or a short, less formal name. If it's a girl, I wouldn't worry about it too much. Many people like different styles of names for different genders. I don't think the boys would mind their sister having a longer, frillier, more formal name as much as they might question their little brother having a name so different than theirs. I think as long as the boys' names go together, your girl's name could be different. If that makes sense?? :)
I don't think you have to stick with nn's for either another boy or girl.
You could branch out a bit with short but full names.
I think you actually have a lot to work with here! Charlie and Sam do sound great with Alex. Daniel isn't bad, but not ideal for the sibset. Nathaniel does sound too formal, but Nathan might work.
other ideas to go with Charlie and Sam:
Jack, Lee, Luke, Drew, Ty, Ben, John, Blake, Clarke, Cody, Jake, Gabe, Shawn, Troy, Zack, Gus, Teddy, Chase, Chance, Theo
As for the girls, the only one I'm not sure really "goes" is Elizabeth. What about just Beth?
Anna, Claire, Leah, Grace, Marie, Mia