You say the encounters are impossible, yet there’s people who have done it with and without cheese gear. There’s even videos on Youtube.
I don’t know the strategy for Balance, but I did the Twins boss as Affliction earlier today and it wasn’t that hard. Took me about 40 tries. With drums, pot, darkglare and dark soul you can burst down Karam pretty fast in the final phase before he gains too much speed. Raest doesn’t oneshot you. His shadow bolts hits for about 20% of your HP after he enrages. You survive by spamming agony on him and the adds to build up life drain stacks, and use phantom singularity on packs. You then slowly and steadily wither Raest down while kiting the adds and placing your pet on the circles. Use mortal coil, life stone, and unending resolve for emergencies.
Don’t know if it’s the intentional strategy or not, but it does work. Raest had a lot less HP on the PTR. During Legion you were meant to burst him down before Karam overwhelmed you.
As for feltotem, you use silence, mortal coil, fear, and stun to interrupt his fel burst. Use DBM to get the timers. Takes some practice to get the rotation right. I haven’t done this one because I think the tauren needs a HP nerf.
If you want to do something on druid, I hear Agatha as feral is the easiest. I can recommend the Ravaged Seed Pot trinket from the first boss in the Emerald Nightmare raid. It’s strong, short cooldown, and great for both Agatha and Sigryn. Try and clear Siege of Orgrimmar and Throne of Thunder to get gear with lots of gem slots.
Here’s a list of useful gems and enchants, if you’ve got the gold for it. https://www.wowhead.com/guides/mage-tower-timewalking-best-enchants-best-gems-best-consumables
Don’t give up too quickly after just a few failures. Practice makes perfect. Read guides and watch videos to help prepare. Good luck.