Not seeing a video I'd be speculating, but it sounds like you're lifting your arms vs. turning your shoulders around your spine, so the shoulders don't really get a chance to move the arms/club slightly to the inside. It also sounds like you're not focused on what the duplessisgolf method is all about, and are trying to direct your arms/club. If you allow the large muscles to take control and not worry about path (in this case the shoulders turning around the spine, and also the shoulders turning the hips a bit at the end of the backswing)... the arms/club will go where they go on the backswing for your swing. Then, on the downswing, if you just unwind your body and turn through, all should return to impact as you started (unless you change something during the swing, like letting the hands or arms get involved.)
The elbows coming back down in front of your body is a "dynamic" moment that just happens as the body unwinds and the arms are free to be brought back down and around to the left (right hander). If you try to focus on returning your elbows back down in front of your body, more that likely, the body will stop and wait for that to happen. It is not something you "do", it is just an understanding of where the body parts are during the swing. Focus on Large Muscles ... Shoulders on the backswing... entire body unwinding and accelerating for the downswing, all the way to the finish. The ball just gets in the way.
Move Less ... Get Good! DUPLESSISGOLF