Viewliner sleepers have standard and deluxe bedrooms. The standard is designed for two people and includes a "restroom" (toilet). I can't imagine more than two people ever getting in one of these tiny rooms (perhaps one adult might squeeze in with two small pre-school children (emphasis on small), but there are only two seats/bunks). The Viewliner deluxe sleeper has a more-proper restroom facility in the room (with shower), and with its additional armchair could easily seat two adults and two children. But, here again there are only the two bunks (though slightly larger). Both rooms are really only intended for two persons in each room; the idea is four people (adults & kids) would need two rooms. To this end, each of the deluxe bedrooms can be combined into a bedroom suite (with a resulting four bunks). The catch is that each Viewliner sleeper only has two deluxe rooms per car (and just 2-3 Viewliners per train), and if even one of those rooms in each car is already reserved, a suite is impossible (book early). Such a suite is also quite expensive.
You can upgrade (at bargain prices) to any available (unsold)accomodation once you are onboard, but with so few deluxe rooms you are often unlikely to find one available for the duration of your trip. Upgrading from coach to standard room is more likely, though of course anything is possible, and there are some really good deals to be had if you care to take the chance. Just always board with the intention of spending the night (or part of the night) in coach, then hope for the best. Naturally, you stand the best chance of getting an upgrade during slow travel periods (beware the first few days of January, Independance Day & all summer, etc.) and by inquiring as early as possible upon boarding.