There is always a chance of an off season snow storm, but not very likely in early Aug. The closer you get to Sept, the more likely, but even by Labor Day it is not common for snow storms. as for cold nights, I typically slept out cowboy style, without a tarp or tent, unless rain was imminent. Never had a problem in Yosemite doing that.
There are tents that can be shared by 2 people that do not weigh 5# or more. If your friends insist on a tent, and are willing to haul it, maybe a trip to REI to check out a rental would be in order.