Yes, Green is an obstruction
to Red and Blue, because both are clear astern and have to keep clear. When
Red establishs an overlap to Blue, Rule 19.2(b) applies and Blue
shall give room for Red to pass between her and Green. Rule 18.2(b) applies between
the boats at the mark.
Room includes the room to comply
with the obligations under the rules of part 2 and Rule 31.