יחיד ששבת בבקעה והקיף מחיצות גרועות כגון שתי בלא ערב או ערב בלא שתי עד סאתים מותר לטלטל בכולו מסאתים ואילך אין מטלטלין בו אלא בארבע וכן הדין אם הם שנים ואם הם שלשה ישראלים חשובים כשיירא ומותר לטלטל בכולו אפילו הוא גדול הרבה ובלבד שלא יקיפו יותר מכדי צרכם שלא ישאר בית סאתים פנוי שאין צריכים לו לתשמיש אבל אם נשאר בית סאתים פנוי אין מטלטלין בכל המוקף אלא בד' אמות במה דברים אמורים כשהקיפו יותר על שש סאין אבל אם לא הקיפו יותר על שש סאין אף על פי שיש סאתים פנוי כיון שהן שלשה מותר: הגה עכו"ם אינו מצטרף לשיירא וי"א דה"ה קטן אינו מצטרף. (רמב"ם פרק י"א):

An individual who spent Shabbat in an open field and surrounded himself with inferior partitions — such as only vertical elements without horizontal, or only horizontal without vertical — up to two se'ah it is permitted to carry throughout; beyond two se'ah one may only carry within four cubits. The same law applies if there are two people. If there are three Jews they are considered a caravan and it is permitted to carry throughout even if the enclosed area is very large, provided they do not enclose more than they need — meaning there should not remain an empty two se'ah area that they do not need for use. But if there does remain an empty two se'ah area, one may only carry within four cubits throughout the enclosed space. This applies when they enclosed more than six se'ah; but if they did not enclose more than six se'ah, even if there is an empty two se'ah area, since there are three people it is permitted. Rema: A non-Jew does not combine to make a caravan, and some say the same applies to a minor. (Rambam ch. 11)

If there were three people who enclosed exactly what they needed and one of them died on Shabbat, they are permitted for the entire Shabbat, since Shabbat began in a state of permissibility. If there were two people who enclosed more than two se'ah and others joined them on Shabbat, it is forbidden, since Shabbat began in a state of prohibition.

If there were three people and each one enclosed his own area side by side and they made an eruv together — if the outer ones are wide and the middle one is narrow, such that the middle one is fully open to the outer ones and the outer ones have walls extending beyond it on each side — they are given their full needs in the middle one even if it is very large, since we view it as if they all dwell within it and there are three together. And also in the outer ones they are given their full needs, since having become a caravan in the middle one, the others are treated as a courtyard to the middle one. Some say the outer ones are only permitted up to two se'ah, and if one of them is more than two se'ah the middle one is also forbidden since it is fully open to it. If the outer ones are fully open to the middle one and the middle one has walls and there is one person in each — each one is only given two se'ah, and if one of the outer ones is more than two se'ah only that one is forbidden; but if the middle one is more than two se'ah the outer ones are also forbidden since they are open to a forbidden area. But if there is one person in each outer one and two in the middle, or two in each outer one and one in the middle — the two outer ones are given their full needs, as everything in the middle is considered as if it were in the outer ones. This applies when they are not open to each other by more than ten handbreadths, for if they are it constitutes a breach and even the walled areas are forbidden. All of this applies when the walls of the smaller one enter into the larger one, and when the walls of the smaller one are set back three handbreadths from the lengthwise walls of the larger one — for then the larger one restricts the smaller one (see above §374:3); otherwise it would appear protruding from outside yet flush from inside and would be treated as a lechi, and all would be considered walled and as if none of them is breached into the other, and each one is only given two se'ah.