I'm going to offer a second route that probably meets most of your requirements while still being within the ability of your group. I am going to give the entry and exit points, and offer some ways of modifying the trip along the way to make it either easier or more challenging once you determine how strong the group is both physically as well as mentally. There is some beautiful cross country above the tree line in alpine terrain that is also very easy. You can attempt it, but there are ways around it that are all on-trail as well. On the map linked below, red represents maintained trail. Orange represents unmapped use trail that is in good condition. Purple represents cross-country. Crimson (brownish dark red) represents an alternative route that is on maintained trail. Yellow represents an old trail that must be avoided at all costs. I have drawn multiple ways to go from entry to exit as well as multiple ways to turn this into a loop of various lengths and difficulties depending once again on group strength and whether you have one vehicle or two.
The entry is at Leavitt Meadows. You could do your acclimatization on the trail because the first part is flat and pretty easy. You could go the short distance to Rosevelt Lake for your first night. Your second day will be flat and soft ground as well.
If you want to do the cross-country element, your intermediate objective will be Dorothy Lake and you have two choices in how to get there. You can stay at lower elevation all the way to Cascade Creek and go up Cascade Falls. On this route, you have a long time to acclimate, but then you do a major trail climb. This is the shortest route to Dorothy. Alternately, you could leave the West Walker for Freemont, Chain of Lakes, Long Lakes, and possibly Cinko (you can shortcut this last one off), then intersect Cascade Creek at higher altitude on the way to Dorothy. This route starts the elevation gain sooner, but spreads it out. It's a longer route to Dorothy, but passes lakes.
From Dorothy, the cross country begins at Stella to Ruth to Helen with easy Class 1 off trail. The col between Helen and Tower Lake is low Class 2 at worst. You have incline, but no obstacles.
From Tower Lake, you can go back on trail, or you can do some more cross-country. I grew up orienteering in southern swamps and some of my time as a guide was spent orienteering off-trail in Appalachian forests, so this was not hard for me. Others might have a difficult time with this if they don't have good sense of direction and elevation change as well as map and compass skills. You depart Tower Lake to the east following countour lines with a very gently descent as you cross-slope through forest. There is much more forest than the map shows. I would put this at low to moderate Class 2. (I did take newbies through here, but they vere very strong. Also, we'd started at Kennedy Meadows and they had 6 days under their belts as well as a climb to just below the summit of Tower Peak.) This XC section eventually intersects a use trail on the headwaters of the West Walker RIver. (The map doesn't have the name of the river written on this section.) Don't camp at the little ponds at the source of the river. They are a mosquito hatchery. BTW, this use trail goes from the confluence with Kirkwood Creek to the top of the pass. Continue up the use trail, going back to high Class 1 XC as you drop into Thompson Canyon. You descend through meadow which flattens and widens where an ancient lake has almost completely eutrophicated and has a meandering stream all through it. I heard there was a large landslide and treefall since I was last there. When you reach this section, camp on a little bluff above it right before it begins. You will have forest to your north and the plain to your south. I have seen black bear in this meadow.
Departing here, backtrack up Thompson Canyon until due west of Peeler Lake. Climb due east XC straight uphill to a col (I don't even know if this qualifies as a col; we always called this a saddle) and then descend the other side, cross Rancheria Creek, and hit the trail to Peeler Lake. You exit from Peeler on trail to Twin Lakes.
Should you decide to do no cross-country, you can take the West Walker to and up Kirkwood Creek, descend Buckeye Creek, turn south and go up gently to Buckeye Pass, then to Peeler. If you get to Tower Lake and don't want to orienteer, descend Tower Creek to Kirkwood and go as described above. You could take the West Walker all the way to its source and do only Thompson Canyon and the saddle to Upper Kerrick Meadow as XC.
If you by any route descend Buckeye Creek, then turn and go toward Buckeye Pass, be warned. The old 15 min. USGS quadrangle of this area has incorrect trail information. The drop out of Peeler Lake is precipitous. Before WWII, there was no trail out of Peeler. The first trail built from this area went over a saddle and down to Barney Lake. Later a trail was constructed from Peeler to Barney with appropriate switchbacks. The trail over the high saddle was abandoned. The old 15 min. quad. shows the old trail and not the new one. (Most other maps have that reversed and are correct.) In 1981, I had that old map and went up that old trail, which was visible on the west slope of the ridge. We followed the old trail to the saddle and started down a steep boulder field that was overgrown with 10 foot high manzanita. The trail disappeared. We bushwacked 1600 ft. straight downhill through brush, hopping from one VW sized boulder to another. Many rocked and some even pivoted as much as 120 degrees. This was one of the most miserable days of backpacking I have ever had.
If you want to go from the Upper Kerrick Meadows area toward Barney and Twin Lakes, take the route by Peeler Lake. (BTW, the small dam on Peeler raises it to an elevation that causes it to have two outlets at opposite sides of the lake. These go on opposite sides of and around an entire mountain range, turning it into an island. Totally weird.)
Don't forget, if you need to create a loop, study the map; there are several ways to do that, both with XC and without. Your emergency exits for most of the distance are back down the West Walker and all the way down Buckeye Creek. (That's easier than going out at Peeler to Twin Lakes, but not as pretty.) No matter where you go, have a great time.
Here's a map of the route:
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