"...Nazi invitations to visit concentration camps" -- perhaps better as "German invitations".
Done
"The prewar Geneva Conventions did not protect civilians, limiting the ICRC's leverage against the German government.[4] However, the ICRC was not limited by the Geneva Conventions..." -- this is a bit confusing since it says that ICRC was both limited and not limited by the convention.
Clarified this.
"...was considered one of the only remaining..." - considered by whom?
It's not clear. Steinacher states that he "was often praised" as such, but he doesn't seem to fully endorse that viewpoint. I added a quote from Favez in a note.
"[ICRC]...discovered that it was possible to send medicines..." and then: "In March 1943, in response to an ICRC inquiry, the DRK stated that it was impossible to send food and medical aid to Theresienstadt", which seems a bit contradictory.
Fixed
"by the Jewish elder" -- does this mean a member of Judenrat?
Yes, added clarification
"secured permission" -- from whom?
Added "from the SS"
"causing an unduly positive impression of Theresienstadt to develop..." -- who developed this impression? the public, Jewish organisations, politicians, etc?
Removed. It's not really clear what Rothkirchen means.
"Rossel claimed" -- perhaps Better "Rossel's report stated..." as "claimed" creates the impression that he was willingly fabricating.