Sour 5 / Sweet 2 (major design change, Sour 5 solution change)
Sweet 2 is still very accessible due to the 50% save required. But it prepares well for Sour 5.

Sour 5 was another story, quite hard now ! I used the "turn a miner with a blocker" trick to save miners needed on the right part of the level. Though the hardest part at the end was to turn that miner so that the crowd does not splat. By some kind of miracle and after many tries, I did it and unwillingly made a precise settings which uses "you fall between diagonal connecting pixels". With this setting, not only the crowd does not splat, but they all fall down in the good direction ! So I even saved a blocker here. Not sure this is intended ?

Sour 6 (design tweaks, solution overhaul). Now I find the level actually easier than before, but this may be because i did not find intended last time and struggled a lot with the timer. I think it is perfectly fine now.
The hardest part for me was to figure out how to save some time at the end : if you set the last delaying basher not high enough, the crowd will make a long way before turning back and you run out of time ! Setting it properly leaves plenty time and I could even save 100%

The clever solution you give makes very little use of the crowd : just need a bomber apart from pionneer. Intended uses the crowd a bit more.
I always think interaction with the crowd is better ; if the pionneer can go in by himself, then the whole "Save One" theme falls apart.
I'll certainly work a bit more on the vertical structure to enforce things. I have to find a way to ensure that if one lemming bashes through the structure, then he cannot stop without using a skill.

Sweet 1 Nice introduction level, open ended. I made it with a single pioneer.

Sweet 2 Lost an awful lot of Lemmings in the pit here, but it is allowed so why not ?

Sweet 3 I save one basher here, with a straightforward solution : see an obstacle, overcome it with a skill.

Sweet 4 Scary level at first sight ! Blocking the crowd and sending a pioneer do the job works well. I get just enough builders but save many destructive skills.

Sweet 5 No comment now, I misjudged the power of stoners !

Sweet 6 Timing the upmost basher is everything here. Probably the intended solution as I have no skill left at the end.
This level reminds me of the newer Lemmings game on Android/iOS : all levels have this vertical setting and screen ratio to fit a phone screen. Is that a coincidence ?

Sour 1 Sweet 1 remixed w/ different skills. I had to struggle a bit to get the half turning lem in time to free the crowd. Good level !

Sour 2 Compression ! I fidgeted a lot to get a first batch of 3 compressed lems to prepare terrain, then compressed the others very tight. Not sure this is intended solution ?

Sour 3 Really love this one Chasm Capers. Spent way too much time building on both sides simultaneously, until I saw a peculiar skill you gave that actually helps with pits...

Sour 4 Sweet 5 remixed. I was scared at first since I could not clear the original level. But then I saw the 4 builders and how to overcome the last pillar so it was a quick solve. Maybe not intended again since I save miner and bomber ?

Sour 5 Pretty sure I backrouted here since I save more lemmings than required, and save skills. The jumper at the beginning survives the fall by one pixel thanks to the miner applied first. I am not really sure how jumpers splat height is calculated...

Sour 6 Probably another backroute. Watch me try to use the shimmier to finally let it fall to its doom ! The crowd is save at the last second of course, I had to adjust some bashers tightly to achieve this.

* Eon 2 Trust Your Lucky Star : at least the talisman requires some trials and errors by the player now.

* One 2 Aquarium Deception : I'm wondering if one can save 3 lems with the same method : try to make the last
3 left bridges at the end to have 3 in the correct diretion. Cannot pull it off yet myself.

* One 4 Clues Do : looks like you're speedrunning this one now! Look at how close the second builder was to the first.

* One 5 Blues : can I ask how you manage to assign the climber to the correct lem with low ID at the end ? I assign it at the beginning of level, before they're all together, to make sure I have a correct one.

Eon 2 Trust Your Lucky Star : changed the vertical structure again, talisman was too easy.
Eon 5 Four Shruggers : worked on the chains to prevent easy ways in them. Beware if you're used to them : Oh No Brick chains do not react as usual.
One 3 Clappy Clapple : tightened things and removed a builder. This breaks the second solution with compression offered by Armani some posts upper. It was cool, but involved the pionneer to go in by himself, and I think interaction is always better.
One 5 Blues : blocked Armani's last backroute to the exit. I must say his solution was very tricky indeed but I fear it may save more than one. Can you find intended ? Easier to execute I think, lems control required.

One 5 Blues : Using nuke seems mandatory indeed because not enough destructive skills. Your solution with flooding a chain then nuke and block near the exit does work, though it could certainly save more than one with a little tweaking and luck.
Maybe I'll work a little more on that, but the number of ways to reach the exit is so big that I'm scared I cannot counter them all.

Intended solution uses the whole level, and control the lemmings so that it is quite impossible to miss the nuke part.