I want to run 4 dcc locomotives.  Now I know I can do so with one controller, but this involves 4 buttons for 4 trains for me to handle.  So could I (how) use 2 controllers each programmed separately for 2 trains and have SOMEONE else  and me each control 2 different trains.....2 operators running 2 different trains...a total of 4 running at the same time

If you're looking at two person operations, it sounds like you're at the point of upgrading to a system with add on throttles. Which elimnates the risks associated with adding a second DCC system to the layout. It also has the added benefit of allowing full control of CV settings when programming locos.

NCE, Digitrax, MRC, and others, make 'entry level' systems with the capability of adding additional throttles for use by other operators. My personal preference is the NCE Power Cab because the add on throttles are identical to the base unit, reducing the learning curve for other operators. And they all operate Bachmann DCC equiped locos just fine.

Len

I have a Digitrax Zephyr (DCS 51, I think) with three throttles connected to it - well four if you count the DT602 as two separate throttles, and it runs just fine. I have a UR90X panel that allows me to also take advantage of wireless infrared if I want. Have had the Zephyr for about 15 years now, no problems yet. Hope this helps.

My N scale layout is using a Digitrax DCS 52.  It has 2 jumper connections to use DC throttles for controlling trains.  But I usually just plug in one of my hand held throttles a DT602 or DT400 that I use for the HO layout.

Another option with Digitrax is the LNWI WiFi interface.  Plugs into o1 of the LocoNet ports and you can use up to 4 compatible mobile Wi-Fi devices and Apps.  Like an Iphone with WiThrottle app. or TCS WiFi Throttles.