Palestrina, for instance, is hard. All polyphony is difficult because it does not consist of an autocratic melody and background, supporting harmonies.
It does not count as Palestrina if the sound goes up to heaven like the shriek of a dying pig. And if this is the case, maybe you should change or update your musical choices somewhat. Not every choir is a painstaking monastical assembly.
This is what Howells is for. Or Purcell. Or even, to a lesser extent, Elgar or Bainton. Easy stuff that you can fake if necessary. Or your Austrian composers--Mozart and Haydn will often work in a pinch because everyone knows how it's supposed to go and will fill in the gaps.
Steer clear of Byrd, Palestrina, and anyone with awkward diphthongs like Messiaen. Avoid elaborate soprano solo bits if your soprano is consistently a quarter step flat.
The sheet music does not guarantee holiness. The execution matters.