By July am guessing you mean the 4th holiday as that is the date the inexperienced usually get surprised with still wet and snowy conditions. Note some lakes in your title post list and some of the suggested lakes are more than 5 miles hikes. And it would be a stretch to reach Rock Creek in 6 hours driving. Am guessing you are planning a short 3 or 4 day trip? Since your friends are newbies, I'd recommend keeping the total vertical climb to under 1500 feet that eliminates some suggested destinations also. When introducing people of average physical condition to backpacking, the prime directive if one has an interest in ever taking them out again is to make your choices as pleasant as possible:
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Distance and vertical climb should be EASY.
The destination ought to be scenic and inspiring to show the value of getting out in the backcountry.
If the weather is foul, do not backpack, do not backpack, and instead car or motel camp per a Plan B.
Avoid mosquitoey destinations because they are miserable to some people even if they have repellant.
A really long drive for a short 3 day trip will gnaw at a new person's patience for such activity.
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Of those mentioned, East Lake is probably your best choice. All the choices may have more mosquitoes early July than are pleasant. I have a suggestion that doesn't fit your criteria:
Out of the Stanislaus NF across Cherry Lake at Shingle Springs Trailhead is an easy trail to a magnificent lower elevation granitoid glacial body of water at 6550 feet in Yosemite National park, Kibbie Lake.
http://mapper.acme.com/?ll=38.05282,-119.84758&z=15&t=T
So why bring 8 newbies to Kibbie?
A short easy drive.
A short 3.5 miles hike with an easy 800 feet of vertical.
There are likely to be far fewer mosquitoes about that lower well dried elevation by early July than higher up at the elevation you noted above 8k.
Lots of nice level granite flats for tenting, most with shade for near lake legal camping.
Easy to obtain the non-quota wilderness permit from Stanislaus National Forest.
Good naturalized self sustaining rainbow trout fishery.
Scenic lake with many glacially carved vertical cliffs plunging right into the lake.
In early July good numbers of wildflowers.
Good dayhikes around parts of the lake.
Nice places to jump in the cool waters and then lay out on smooth clean granite.