In the case of In re Cassese, Bkrtcy.D.Mass. 2002, 286 B.R. 472, the federal court held that under Massachusetts law, an owner/cotenant, who was not already protected by being in the same family as the initial homestead declarant, may file a separate homestead declaration on the same property for the benefit of his or her separate family, the court holding that it is only a cotenant who is already covered by an existing homestead exemption filed by a family member (such as a husband or wife), who may not file a separate homestead. Assuming that "friends" (no matter how friendly they are) don't constitute a "family," then it would appear under this ruling that two owners could declare separate declarations. On the other hand if they do constitute a "family" then it would seem under G.L.c. 188, §2 ("The acquisition of a new estate or claim of homestead shall defeat and discharge any such previous estate." See also, Garran v. Citizens Bank of Massachusetts, Bkrtcy.D.Mass.2002, 280 B.R. 292, affirmed 338 F.3rd 1.) that the second homestead would trump the first.
The only cases that have interpreted the statute regarding this issue are federal courts (with the one exception I'm aware of being Dwyer v. Cempellin, 424 Mass. 26, 673 N.E.2d 863 (1996), which concerned a question certified by the federal court to the Supreme Judicial Court on a joint declaration of homestead), so its unclear at this time whether the Supreme Judicial Court would concur with the results.