Our class C has dual rear wheels. When we are parked at a site, do we need to place leveling blocks under both tires on each side, or is it acceptable to block up just one tire?
I took it that the OP was asking about blocking both dual wheels on a side. Answer to that is yes it's a good idea to do it.
Although I came across a video the other day of an rv dealership showing how to set up a TT. The TT had tandem axles. They guy only put leveling blocks underneath one wheel.