דלא תחזקו אהדדי – That you should not establish rights of possession against each other.
רש"י maintains that since there were no witnesses that the brothers were partners therefore either could have made a חזקה.
The ר"י maintains that there were עדים, and nevertheless they did not want that either should possess the maid for three years, lest people forget that they were partners.
אבל כתוב עיטרא קלא אית ליה – However if a contract of division of labor was written up, then it is publicized.
An עיטרא, while able to publicize a partnership, is however not considered sufficiently reliable in the case of minor orphans. Therefore a relative is not permitted to administrate the properties of a minor orphan, lest he claim them as his own.