I am learning how to spot steinkerns, and I believe that all of these are examples. The first set of three would be gastropods, I think, and the set of two smaller ones are possibly phosphatic steinkerns of coral. I am not certain.
[These come from an estate collection I acquired last year, all unidentified but labeled as coming from Edisto Beach, SC on dates ranging from the late 1970s through the early 1990s.]