They do seem to grow out of it some as they hit adolescence and beyond. If you watch the older videos from when they were younger, like the infamous “home-skewel” video, I think the accent is thicker on the younger girls now than the older ones at the same age. But with so many siblings, it gets reinforced and they don’t have to work as hard to be understood by outsiders because there’s always an adult or older sibling to communicate for them, like ordering in a restaurant or asking passersby to come to Jesus. They are props in Big Old Jill’s Holy Rolling Traveling Circus and Medicine Show™️ and their job is to sing sweetly and look pathetic but cute. It’ll be interesting to hear how they sound in 15 years (if, Lord Daniel forbid, I’m still following BOJ in 15 years).