Okay, "3 Women"... What WAS That Ending?!

So, I'm on this classic movie kick and decided to watch Robert Altman's "3 Women" (1977) based on a recommendation. I gotta admit, I'm still trying to wrap my head around it. Shelley Duvall is amazing as Millie, this kinda desperate and delusional woman, like she's trying so hard to be someone she's not. And Sissy Spacek as Pinky...wow. Just wow. That character is so weird and unsettling from the start, but then things just get... weirder. I was totally hooked on the character dynamic between Millie and Pinky living at the Purple Sage, and the unsettling way Pinky tries to become Millie. I was expecting it to veer into a thriller or something, but when the whole pregnancy/shooting thing happened, honestly, I was just lost. I'm all for ambiguous endings, but I'm not sure I even understood what happened! And the third woman, Willie (Janice Rule), mostly paints those creepy murals. I get that she's supposed to be important, but I'm not sure how. Is she a mother figure? Is she just another weird thread in this dream logic tapestry? So, here's my question for anyone who's seen it: What's your interpretation of that freaky ending? Specifically, what's the deal with the role reversal and the ritualistic stuff? Am I just missing something obvious? I need some explaining of how these 3 women become "family".