Having been to the Rockies a few dozen times, here are a few thoughts:

1) The Rocky Mountaineer is a great experience, but it's certainly not cheap. There are hundreds of different packages they offer depending on itinerary, number of nights you want to spend at a hotel, included activities.

2) Traditionally, I've found that I could piece together a much cheaper package by booking the hotels and activities myself; this may not necessarily be the case this year since hotel prices this summer are higher than I've ever seen them before. Also, booking this close in, the question may be: "Will I get any availability booking myself?" (Rocky Mountaineer blocks many rooms, so should be easier)

3) Banff: Yes, the Fairmont is definitely your best option

4) Lake Louise: It's much trickier. I'd argue:

Fairmont Gold room/suites >
Fairmont Jr. Suite / One-Bedroom Suite Lakeview >
Post Hotel >
Fairmont rooms & non-view rooms

The entry-level rooms at the Fairmont LL are tiny and very worn (they're used for the tens of thousands of tourists who booked a via tour operator etc.). Similar could be said about the entry-level rooms at the Fairmont Banff Springs.

5) If they take a train in one direction, consider driving (being driven) the Icefield Parkway between Banff/Lake Louise and Jasper (one of the most scenic drives you'll get to experience), spend a few days there and then fly out of Edmonton