I am having trouble finding anything out about the surname Nesselrothees. My great grandmother was registered under the surname in 1840 England. Her father was Alexander Dorow Nesselrothees. He was apparently from Frankfurt.
If the family origin is indeed Germany, the name Nesselrothees reminds me of the German nobel family of Nesselrode. There is an extensive Wikipedia article (in German) on this family: Nesselrode (Adelsgeschlecht). Please provide more information on your great-great-grandfather, e.g. by linking sources. If there is a sourced link to Germany, I can maybe help with further research ideas to connect the name to the family mentioned above. The family name Nesselrode comes from Nessel (“nettel”) and -rodung, an suffix meaning “clearing”. The place linked to the family origins is Nesselrath, also referred to as Nesselrode in medieval times.
The original spelling may have been "Nesselrath". A search for "Nesselr*" in the Historic German addressbooks includes a number of Nesselrath entries, and some additional variants: Nesselrat, Nesselroda, Nesselrode, Nesselrodt, Nesselroth
Since "Nessel" is also a surname, consider that "Nesselrothees" may have been a hyphenated name. Although "Rothees" does not appear in the previously referenced database, Rothes does: thus "Nessel-Rothes".
A final consideration: there are 2 German cities named Frankfurt, and a number of smaller placenames that include Frankfurt in the name.
It has taken me over 20 years to find my great grandmothers birth the reason being I have been looking for her under the surname Wolff which is the name she and her family were using on the 1851 English Census. I have since found 6 of her siblings registered under the name Nesselrothees. I have her birth certificate and have ordered some of the others. I have 6 births and one death under the name Nesselrothees and maybe 4 births and 2 deaths under the name Wolff. Her fathers name on the 1851 census was Alexander Heinrich Wolff born Frankfurt on the Mein, occupation Professor of Piano Forte. He died in 1855. He was 20 years older than his wife and in saying that I can't find a marriage for them.