Question juridique clé
Whether the action seeking nullity of the entire auction sale was wrongly directed against only one co-buyer.
Solution extraite
Yes. All co-buyers had to be sued together because the challenged sale created a single legal relationship that could not be set aside only against one purchaser.
Motifs extraits
If the buyers held the property jointly, necessary passive joinder followed from joint ownership; if they held distinct co-ownership shares, the sale was divisible, but the factual record was insufficient to determine which regime applied. For the first subsidiary claim, the cantonal court was correct to reject the action, since it was not brought against all co-buyers.