1: They used to sleep until noon before they had a baby. Or: They used to sleep till noon until they had a baby. 2:There used to be a theatre in our town, but it closed down three years ago. It’s tricky but we don’t typically use the “had” when using “used to”!

Past perfect would be had slept. It doesn’t work in your sentence. Here’s a sentence using had slept. We had always slept deeply until the baby arrived and now we sleep lightly. There had been a theater in our town, but it closed down 3 years ago.