Some chants, in order of difficulty (IMO) Veni Creator Spiritus Adoro te devote Salve Regina Pange lingua
These are the top of the "top 40" chant hymns known to Catholics world-wide, and can connect you to people in prayer in all of your pilgrim experiences.
Get some good recordings that don't feel too high or two low or too slow when you hum along. You tube has some, for example. A small group will benefit from quicker pacing.
Ask a musician you know to help you determine a starting pitch, and a way to give that pitch, for example, a pitch pipe.
Go through the Latin text, pronouncing it slowly, one verse at a time. Pray through the translation of each verse as well.
I taught one of my scholas the Anima Christi from the PBC, which I used after the communion chant was finished as a chant "motet" of sorts. Latin and the length might make it a bit difficult for the congregation to learn, but if you have a schola or core group, it might be perfect, from what I know about you.
Start with some of the classic devotional hymns and chants: Adoro te devote Jesu dulcis memoria Ave verum corpus Salve, Regina
They all have beautiful, simple melodies; and phrases that aren't very long, so that beginner singers won't have any trouble with breath. You can find English translations of these also, sometimes right in your parish hymnal or "missalette".
You'll have to choose a starting pitch for each piece to make its vocal range comfortable for you and for your group. Once you decide on that pitch for each piece, you can play it on a piano (if you have one handy), or a pitch-pipe (about $15), or get a free smartphone app like "xPiano" that displays a piano-style keyboard and lets you tap it for the note you want.
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