Yeah, you can probably skip Luke Cage as it's not important to the storyline if you've got the basics of the character and his abilities. Jessica's Jones also not essential (other than the fact that it's great and no one should skip it); all that would really be missed from that is the back-story between Jessica and Luke, but they hint at it enough to get the idea anyway.
If you've not watched Iron Fist then... Tbh... It'll probably be a chore trying to figure out Wtf is actually going on. I'd say this is a direct sequel to both Iron Fist and S2 Daredevil, and having seen both is pretty important.
Spoiler:
And actually having just said that has made me realise that this is basically a combination of mini Iron Fist Season 2 and mini Daredevil Season 3, feat. Jessica Jones and Luke Cage in supporting roles.
. Throughout the whole thing they're both basically like "Well I have absolutely no idea what the **** is happening but these seem like bad guys and we're super strong so I guess we'll hit them and stuff."
All of the villains are DD and IF, and even other characters... Stick, Elektra and Colleen Wing feature heavily, characters from other shows are basically extended cameos, even Misty tbh. Obviously there's also Claire but - although her "main" role so far was arguably in Luke Cage - she was a DD original and actually probably played a more pivotal role in Iron Fist than she did in Cage...