Although both talk about the future, they are very different. “Is to come” is more of a hope or expectation. An example is “the best is yet to come”. “Is coming” is more like a prediction, or informing you of what will happen soon. “Where is his Lordship?” “ He is (just) coming.”

Come : To move or travel towards or into a place. (VERB) Coming: The act of arriving; an arrival. (ADJECTIVE) I hope I've helped ❤️

Context is always important, but here are the basic uses. Students are to arrive by 9 a.m. Monday. [obligation] Students are arriving by 9 a.m. Monday. [arrangement] Stusents are arriving (now). [action in progress] More information: www.ef.com/ca/english-resources/english-grammar/future