One of the things I run into often with conducting choirs is building and rebuilding. Building a choir is almost easier that rebuilding one. Rebuilding a choir is like getting your stick shift car up to 4th gear and then having to stop at a stop light, so you have to start all over again in 1st gear.
One thing remains the same between the two, however. You must strike the balance between too difficult and too easy. As a musician, I have done quite a lot of choral work. I have a large repertoire to work with, but most of it is too difficult to spring on a "seedling choir". It's like watering seedlings in the heat of the day. If you water them at 4 in the afternoon, all that water is going to boil the leaves as it evaporates. You water in the morning and the evening, when the sun won't make them in to boiled greens. So it is with a choir.
Start with the basics: good vocal exercises and practices. Teach them to breathe and then teach them how to hold their mouths. They will always be better off for this. Always remember to reference exercises that you did during the rehearsal to reinforce that those exercises are important to their skill building.
Move slowly toward parts singing. Even if you only have two or three people, you can sing in parts. If they have never sung in parts before, teach them to sing a round, first. A really good resource for sacred and secular rounds (in a few different languages) is 'The Kemp Family Collection of Rounds, Canons and Songs". There are varying degrees of difficulty within this collection to keep you happy for a while. Also, another valuable resource for sacred musicians are the collections from Taize. These, again, are varied in their degree of difficulty and get people into the habit of hearing their own part.
Be careful not to move too slowly or too quickly. It is not advisable to go from a rousing rendition of "Row, Row, Row Your Boat" to "April is in My Mistress' Face". Unless your choir is full of prodigies, there will be a few years of separation between these pieces. But, you don't want to be doing "Frere Jacques" the second year of your choir, either. Progress. Let them grow.