propane regulation ?

I have a small propane system set-up in a remote off-grid cabin where the regulator and outside piping hasn't been changed since before we brought the property. The propane fuels the 1950s-60s gas 4-burner and oven range, the refrigerator, and 2 propane lights. The original tank was a 60lb tank, and we now cycle between a 30lb tank and a 20lb back-up to make it easier to lift and take in to town to refill. Inside the cabin the exterior hose connects to a 1/2" black iron manifold with separate take-offs to the range and the fridge (standard yellow sleeved gas lines with shutoffs and leak-detector automatic shutoff valves) and an additional shutoff to a 1/4" flex copper line to the 2 lights. Outside the tank connects to a regulator (Marshall model 260, 2-stage lp reg, listed 605H, outdoor use) and then to a standard 1/4" POL rubber hose. Question is, is the regulator and POL hose the correctly rated regulator and connection to the cabin? We need to replace them due to age and rubber gasket/hose decay, they are both due, but we don't want to replace them for "like" items if they weren't correct from the get-go. Everything "works" but the flame on the range has always been finicky (might just be the range) the burners only seem to work on full high or full low, mid-ranges the gas flame flickers and dies out. I'm really wondering if the 1/4" outside line isn't able to fully deliver enough gas for the 1/2" inside appliance line. I'd appreciate it if anyone with propane regulation experience can help steer me in the right direction.