Hi Henry,
I travel coach exclusively so maybe I can help you a little.
The train you'll be taking is a double decker Superliner, it's very roomy.
There are shelves on the lower level for baggage, it's a little tight sometimes but the Conductors or Coach Attendants will guide you when you get on.
Don't pack too much and you'll be fine.
There is also a lot of room above the seats - nothing at all like the airlines - for more carry on luggage.
You'll also have room under your seat and on the floor in front of your seat for smaller bags.
It couldn't hurt to call Amtrak's Customer Service - 1-800-USA-RAIL- and tell them that you need 6 seats together - they should be able to convey that to the Conductor and Staff.
I've seen seats reserved for groups on almost every train I've been on and I'd say that you guys are a small group.
Every one of the trains I was on last month were sold out and seats were also assigned on every train, so there weren't people scattered all over.
They did a good job of keeping groups of seats open for people traveling together.
Don't let others scare you into the need for a bedroom, if you can go with the flow, you'll be able to sleep in a coach seat with no problem - then you can freshen up when you get to Reno.
You'll be able to move around the train all you want and you guys will probably spend most of your time in the Sightseer Lounge anyway watching all the fantastic scenery.
I don't know if you've taken the train before but here are some photos to give you an idea of what you can expect.
Luggage racks above the seats on the California Zephyr
Coach seats upright
Coach seats reclined with all of the gee-gaws extended
And my favorite place on the train.... the Sightseer Lounge (SSL on the forum)
Your trip is going to be fantastic!
Don't hesitate to ask more questions, most everyone here is very helpful.