I think Grant works well with Griffin and Grace. I also like Graham and Grover with Griffin and Grace.
You may also want to consider names that begin with G but not the Gr.
Griffin, Grace, and Glenn
Griffin, Grace, and Gavin
Griffin, Grace, and Garrett
Griffin, Grace, and Guthrie
For names similar to Cohen, consider Colton, Collin, or Coleman - all of which the nn Coe would work.
I love Grant or Graham (or Graeme), maybe even Graydon or Gregor. Good luck!
I like Garret or Grey, to continue the G names :)
Oooh, I love Griffin and Grace together!
Grant fits well if you want to continue the G/Gr theme. With three Gr's, though, it might be too much? Personally, I'd prefer a different beginning sound.
I second the votes for Graham (although I like the Scottish spelling, Graeme) and Grant.
I would suggest Gavin but if you want to continue the Gr- theme then I would consider Graham or Gray.
I think Grant, Gavin, or Gideon could all work.
I think close to Cohen in terms of rhythm (but nicer as a given name) something like Callum, Corbin, Cillian or Cianán?
If you like the name Cohen, use it. There is nothing "offensive" about people who use it. In Latin America Roman Catholicism is the predominant religion, and "Jesus" is a common and honorable name. "Mary" is another name frequently used by Catholics even though it is their belief that Mary was "immaculately" chosen and distinguished by God in perfection.
Cohen is no different than using "Dick" as a nickname for Richard. It's only offensive to people who inflexibly assume that the world revolves around them and that a stranger's name choice was intentionally chosen to offed them. I did not know that "Cohen" could potentially be perceived as distasteful, and I always associated it with poet and musician Leonard Cohen. If I had chosen to use the name it would be in honor of a poet and have nothing to do with Judaism. The world is not black and white. And it does not revolve around you. Or Jewish people. Or "Dick's" who cannot conceptualize that a name or word can have different meanings used in different contexts.
My first thought was Gabriel.