I'm reading the Silmarillion and a small thought hit me while I was reading and it just grew, what if Miriel lived and Finwe died but Miriel remarried.
During Feanor's birth Miriel was weakened so instead of watching his wife fade Finwe was able to give the power of his fea to try and keep her alive. He gives yo much of himself and fades. Miriel lives but is still weary but she stays to raise her son.
Eventually she does remarry because of her weakened state she needs help ruleing her people and raising her son. So she does. She still has Fingolfin, Finarfin and Findis but would Feanor love them as his siblings because they have the same mother and he's trying to ignore that fact they have different fathers? Would Feanor treat his mother differently after she remarried and see his half siblings as a betrayal to his father? What are your thoughts on this?
Okay, so the first part of this scenario - Finwe giving his life to save his wife - I can absolutely see.
The rest of it is where this gets tricky.
Because while, canonically, Finwe did eventually decide it was better to just stay dead, this happened only after (a) everything in his life had gone pretty catastrophically wrong, and (b) it was the only way to let Miriel return to life. In this situation, neither is true, so I think if Finwe died then, he would want to return to life as soon as possible.
It’s possible, however, that the effort of giving so much of his fëa would leave him as weary as Miriel canonically is, so let’s say that happens, and Finwe is convinced he’ll never recover enough to return to life.
(Someone, fact checking this with Mandos: Is that true?)
(Mandos, having dealt with extraordinarily few dead people at this point in the timeline: . . . After such an event, he will never be the same.)
(This is not actually helpful.)
. . . Which would presumably throw all the elves into a tizzy because if Finwe is gone and never coming back, who’s in charge? Miriel? Feanaro, once he comes of age? (Fun fact: I bet he would go by Curufinwe in this ‘verse.) They don’t have a stye of inheritance set up yet! Last time they just picked a competent guy to be in charge because he was the one brave enough to head off to Aman first! Should they hold some kind of competition and choose again?
Miriel is a plausible winner of this political knot, either in her own right or as a regent for her son. But - unlike in many historical human societies - I don’t think there would have been any pressure for her to remarry. If the elves really wanted a male ruler, all they’d have to do was wait for Curufinwe to grow up, after all. Miriel needing help is perfectly plausible, but I don’t think she’d necessarily have to marry to get it. If she has family, they can help with raising Curufinwe; if she doesn’t, I’m sure there are plenty of people ready to volunteer. If she needs support politically, she can get a council or a chancellor or a series of look alikes to pretend to be her.
Or, you know, they’re elves. They have forever. There are a lot of problems she could probably just . . . slow down and deal with over a longer period with plenty of rest breaks.
In fact, I think there would be a lot of pressure against her remarrying. Both because of all the reasons Finwe would have received such pressure (it’s never been done before, it’ll prevent the spouse from having the opportunity to change their minds, etc.), and also because it would further complicate the question of who’s in charge and because in this AU Finwe died for her. Moving on from that in a way that blocks him from forever returning is going to be even worse PR than Finwe doing it.
But maybe Miriel just wants to! Maybe she’s lonely! Maybe she’s fallen in love again! Maybe someone else gains strong political support in the post-Finwe mess and she invents the idea of a political marriage!
(For symmetry reasons, I kind of want this guy to be Ingwion, but it certainly doesn’t have to be.)
Whatever her reasons, she does it.
Having kids is going to be . . . tricky, since elves have to actively choose to have children, Miriel would presumably be the one bearing them and that almost killed her last time, and she’s still weakened from that, but again - maybe they really want them! Maybe Miriel is actually passively suicidal! Maybe she’s cunningly homicidal, and she’s actually plotting to lure her new husband to his death in the same way Finwe died . . .
Or maybe she’s just recovered by now and is confident that things will be different this time, and you know what, they are.
But to get to your actual question: I think Curufinwe would hate his stepparent exactly as much as he does in canon, with possible bonus hatred if he perceives this stepparent as having stolen his throne. I don’t think this would be reflected onto Miriel for the same reasons it wasn’t reflected onto Finwe in canon, and also because he would very much feel like his mother’s difficult health was All His Fault and feel incredibly guilty for it.
As for his siblings . . . My instinct is to say that would go better than canon, but that’s probably just because (a) of the stereotype of women being better communicators, and (b) because it would be hard for that to go worse, but honestly, I think you could spin it either way, especially if he initially perceives those children as a threat to his mother’s health and then gains new levels of guilt and self-hatred when they aren’t.