Is it mandatory to have other players for this questline, or is it possible to solo it granted it will take a while?
You can solo most of it, but it will definitely take longer.
You will need to be in a raid to tether to and defeat the first three raid bosses in Amirdrassil for one part of the questiline. That is the only part that definitely would require a group.
Superbloom collection will be slower outside of a raid group if the group does not reach the purple bag, but if time is not an issue, you can do it with whoever is on your realm group.
You will need to defeat rare mobs, but those are soloable with some gear, and you can avoid the large rares that show on the larger map that require events to spawn. Small elites marked by star icons on the map, including lashers from the emerald frenzy, are more manageable.
You will need a leatherworker, scribe, and enchanter to craft an item for you, but if you really want to go solo, and don’t care about progress earned on a currently-trained profession, I believe you could unlearn your current profession then learn and unlearn each of the needed professions on your character going through the questline. I made an evoker alt on my second account so they could learn and unlearn all three to craft mine since my fellow crafting friends have been AFK for the past few weeks. You only need skill level 1 in DF profs for this. I didn’t try it on my character doing the questline, though, so I’m not sure if there are any additional limitations.
To avoid needing a healer for the grip attunement, you can do a daily quest to obtain a salve to prevent damage, you will just be limited to 30% completion a day.
I just did a writeup on wowhead comments after I finished my quest the other day if it helps. I plan to link the info on other quests as well hoping it helps latecomers like me.