see "Lies they tell.." for suitable material.
And, of course, have each party emphasise that they are perfectly ready to be united with the others, as soon as they see the error of their ways and come back to sound doctrine and practice.
After all, the building is the proper place to preach (even though no outsiders can hear), to share (even though there's no one to share with) and to teach (even though no one is learning). Anyway, it's scary outside - you might meet criticism - you might meet real people - you might even meet Jesus...
Thereby inflating their egos, encouraging teachings that assert their own authority and deny the freedom of the Gospel, and making church rank attractive to control freaks, atheist snobs and materialist moneygrubbers.
You do have to phrase this right. It's not "church possessions" it's "church resources"; and it's not "church buildings" it's "investment in the Lord's work". Either way as soon as these things become important you are hanging a millstone round the Church's neck.
Not one in ten of Christians can give a clear and reasonably watertight definition of "priesthood of all believers", of "election", of "apostolic succession", of "the supreme authority of scripture" or of "the traditional view of the Church". And I do mean "or" - just one each will do. But how important these phrases are as battlecries!
This deserves a ten in its own right...
Everybody used to say they were Christian, so it wasn't worth mentioning. Nowadays it is worth mentioning, but we seem to have got out of the habit...
So don't sing 'Guide me, O Thou Great Jehovah', it's oldfashioned. Don't preach - it's oldfashioned. Don't teach basic doctrine - it's ...
It may come as a surprise, but there is nothing in the Bible that says we have to have services only on a Sunday, or that a service has to contain a sermon or a eucharist/Lord's supper/breaking of bread; or that we have to use methods of communication that were oldfashioned a century ago. What was 'good enough for us' is not 'good enough for nowadays' (the whole thinking behind the word 'good' in this context is unscriptural). And 'oldfashioned preaching' is not the recipe for refilling the church - after all, that's what emptied them in the first place.