You could hire a car - shouldn't be too bad between four of you. And drive from Calgary to Banff and the Rockies and then on to Vancouver, then fly out of Vancouver back to Heathrow. Some car hire companies are cool with one-way hires. (NB Virgin are starting London to Vancouver flights sometime this year.) And camping in the National Parks and Provincial Parks is pretty good. You can have fires in the fire pits, although the National Parks charge extra (certainly Banff and Jasper do) for a fire "permit" but you do get "free" firewood included. If you're camping swot up on being "Bear Aware", unless you already are from your last trip! If you fancy sharing a room with your buddies you can get rooms with two double beds at various motels and hotels which can ease the cost.
The drive into Vancouver from the north via Lillooet is stunning (as is much of B.C.) but this is especially good.
In and around Banff I mostly hiked so can't offer too much there. I guess you visited Lake Louise last time in the Rockies? Certainly worth a look and a hike or two. There are some nice short hikes off from the Icefield Parkway if you're into that. The Edith Cavell and Angel glaciers up around Jasper I thought was way way better than getting the n-wheel-drive trip out on to the Athabasca glacier on the Columbia Icefield from the Icefield Parkway. YMMV.
In Vancouver - the Sun Yat Sen Garden is good for a bit of peace from Vancouver for a couple of hours, in Chinatown. The Buddhist Temple in Richmond (one of the 'burbs) is worth a visit, as is Granville Island and the Museum of Anthropology. The Visitor Center at Canada Place will provide loads of ideas for other stuff to do. If you're into camping and all sorts of outdoor stuff go and be awed at MEC on Broadway.
If you don't have a car in Vancouver the buses and the Skytrain will get you around. You can get a network map for a very few dollars from a number of places. The tickets are zoned so you can swap from bus to train and back for, I think, 90 minutes within your purchased zones. I'm expect that you can probably get day/week tickets too. If you do have a car make sure your hotel/motel has allotted parking.
If you plan on taking your laptop you can generally get free internet from the Public Libraries, although sometimes this is time-limited. Also some Visitor Centres provide it too.
Have a great trip!
