Level 8 "Lemmings Are Grounded": not yet solved. I am assuming that the solution involves an advance lemming going along the top, mining to the right and then being turned by a Blocker which climbs up the wall, then a Basher to free the Blocker & get the group to the exit.
Level 9 "All Stepping Stones Don't Help": I had problems with this because of a false assumption on my part. I thought that Sliders would splat if they descended from a platform, where the distance from the underside of the platform to the landing ground is 3 pixels more than the distance from the bottom of the splat ruler to the pink mark. But they don't - even when the Slider's lower foot (in the final frame before it transitions to a faller) is 1 pixel higher than the pink mark, with the splat ruler anchored on the ground. Once I realised this – thanks to a sneak preview of part of Master88's solution – it just needed some experimentation to find a solution. As Master88 says, there is more than one possible solution.

Level 11 "Turbo Tunnel": this level is all about meeting the time limit. A trial run shows that it is not possible for the last lemmings to reach the lower exit within the time limit. From this it follows that they must aim for the other exit; and this dictates how 3 of the skills must be assigned. The remaining challenge is to ensure that those lemmings that are reversed while obstacles are being removed are themselves halted and re-reversed in good time. Timing is very tight – I had less than a second to spare – but there is ample scope for tweaking the timing and positioning of the manoeuvre that delivers the re-reversing in good time. 
Level 12 "Season Of Miners": I found it relatively straightforward to save all but 1 lemmings. The problem arises at the end, where advance lemmings - that mine back away from the exit - have to be halted and reversed. It took me some time to find a workable option for removing the Blocker – requiring careful attention to detail to economise on miners. Timing not so tight here.
Level 13 "Walking On Hot Coals": an amazingly easy level, solved with quite a few skills to spare. Presumably a backroute.
Level 14 "Methods Of Masters": not yet solved. It is easy to see where the Cloner should be used to help create a route for a Basher to get through both central blocks – but very difficult to implement.
Level 15 "Final Trick": another level where you can easily fall 1 short of the save requirement. Looks like it needs a clever trick with the 2 Platformers, but I don't know a trick that helps here.