Hi all,
I'm not an expert on names but if you receive an e-mail from Christiane you may notice the Stoelk name with the umlaut (Stölk).

When you remove the umlaut you add an e so you get Stoelk.

The Kusel name is sometimes spelled with the umlaut so you have Küsel.
Küsel would be spelled Kuesel when you drop the umlaut.

Many German immigrants dropped the umlaut or it was dropped in the immigration records and many times the (e) was not included so you need to check older records or records in Germany to see what variation of spelling your name might have been.