his disciples

The word "his" refers to Jesus.

while the doors were closed

You can translate this in an active form. AT: "when they had locked the doors" (See: rc://en/ta/man/translate/figs-activepassive)

This is a common greeting that means "May God give you peace" .

"without belief" or "without faith"

Here "believe" means to trust in Jesus. AT: "put your trust in me" (See: rc://en/ta/man/translate/figs-explicit)