MB4 246b: Multiple Adjoining Yards (378:1-4 - part 1)

If several chatzerot open to each other and each chatzer also opens to reshut harabim or mavui: Can the middle courtyard make 2 separate eruvin with 1 and with 3?

Making an eruv where an inner courtyard is only accessible from reshut harabim via an outer courtyard: What if one of the courtyards doesn't have an eruv - who can and can't carry?

What if an inner and outer courtyard made a joint eruv but they forgot to include one person, who can/can't carry?

If there is only one person in the inner courtyard can he ruin the eruv for the resident(s) of the outer courtyard?