Bachman or digitrax zephyr for home layout

Problems with couplers, For some reason on my cars the couplers won't stay Hooked up or one coupler sits higher or lower. I am using Kaydee couplers installed on my cars by a local hobby shop. some couplers are frame mounted and some are truck mounted. Can someone tell me the cure. I know one sure cure, buy new Bachmann Cars and stuff only

I am new to scale model railroading, I bought 2 HO Bachmann item number66802 NS engines. they have the same road numbers 5555. I have been running them on my home layout on dc using 2 separate controllers, but I recently joined a local railroad club. and they let me use a digitrax DCC controller. my queation is, How can I change the volume on the horn as well as the bell. At the club everybody else horn and bell can be hear at lot better than mine TIA