Over a piece of property? I doubt a dispute over a piece of property is jeopardizing anybody's immortal soul. Besides, they can receive the sacraments at another parish where they are not known.
Yup, Sinky, over a piece of property.
Check the Decalogue, which hasn't changed all that much. Your position amounts to "[those parishioners] stole it, FAIR AND SQUARE."
But, Sink, they DID steal it...
BTW, the old Canon Law provided an automatic excommunication for anyone suing the Church in the secular court system (bringing the Church under the jurisdiction of the gummint courts and subject the Church to discovery for fishing expeditions into Church records). JP II has been entirely too kind to the miscreants by removing the automatic excommuncation.
Finally, the unworthy receiving of the Eucharist by the directors of this rebellious corporation is itself the grave matter which necessarily underlies mortal sin. There are obviously requirements of knowledge of gravity and intent. Intent seems clear in such an event. Their only out would seem to be ignorance and that ought not to be wilful. They can also embezzle the funds of others entrusted to them (a mere??? property crime and sin), rob banks, desecrate the Eucharist, rape, abort or engage in lavender, ummmm, relations if they so choose. That some bad behavior may be chosen by anyone merely reflects the free will bestowed on each of us by God. That one has free will does not guarantee salvation despite unrepented gravely immoral behavior.