You're both in your forties. Her parents' opinion shouldn't even matter.

And if their opinion is crucial for your girlfriend, I'd view that as a huge red flag. She's not a kid who needs mommy and daddy's approval to date, or to move in with you.

And if she thinks she needs their approval now, what else will she need their approval for?

Her parents honestly sound very rude and controlling. Sounds like they (and your girlfriend, probably) have a lot of growing up to do.

If your girlfriend requires you to win over her parents, I'd leave her.

Why hasn't her parents shunned their daughter AND her ex husband since they sinned the an awful, unforgiving sin in the eyes of "their" church.

One can not shun in part.

Do you see what I mean?

What do YOU know about the sect they belong to. I use that term for a specific reason.

Tomatoe---I realize they want the back together.

However IF IN FACT the sect is a firm believer and I do mean following strict rules THEY would have booted them out of the church because of the divorce.

I am trying to find out by OP what sect/church it is.

Cant have it both ways. Either they are against Divorce OR they are not.

WHAT is the name of this Religion?

OK I am taking the chance of being booted off Step talk. Here is goes.

OP get over it. Unless you refused to discuss with your girlfriend about her parents core beliefs, isn't it true that YOU decided that she,, with all her background, and upbringing , has to be the one for you. YOU knew this walking thru these many months.

Her parents will NOT accept you. So go ahead---stick with it. Sounds like a great foundation for a successful relationship.

SMH

I miss people having common sense.

Really the issue here is you thinking you can change the opinions of people who are staunchly entrenched in their religion. The parents beliefs are not going to change just because you want them too. As for the girlfriend it sounds like she it doing whatever she wants. IMO the real issue here is you want the parents to change their morals and values to suit yours, and it's not going to happen.

You can't ruin the relationship between your g/f and her parents. They already think she's a sinner so there is already bad blood there. I know you probably love your g/f and would love for this situation to get better but its already starting off pretty awful (unacceptance, threats, not cordial, etc). Imagine how much worse it will get if you move in together? They might disown her who knows. Either way, its up to her to manage and mediate the relationship between herself and her parents. Its not too late to walk away because you are in for years of heartache and turmoil with this one, if you both allow her family to dictate your lives in any way.

never underestimate the power of parents and skids to make your life miserable.

ideally the partner or spouse would be able to make up his or her mind about the relationship but its not as easy as that.

there are not easy answers.

This is trouble for so many reasons.
She is in her 40s and still financially reliant on her parents - not good. In turn, the parents have no problem asserting the control she's given them by living off them. Scary!
The parents might make good on their promise and accuse her of things regarding her kids that will force her to leave you or leave them. Either way, that will be ugly.
Even if you do manage to be together, the ex will be a bigger part of your life than normal (which normally is way too much) if the parents harbor him and reject you.
She is from a freaky religion that you should probably share or at least be inclined toward to make this work - but instead, not only aren't you talking about marriage, you're talking about shacking up. Yea, not so 17th century.
And then there's this: if she's so religious, why DID she get divorced? Why would she even THINK of shacking up if she's so religious? There's something off with her claiming this religion but doing so many things the church opposes. Seems she's taking what she wants from her church and leaving the rest. That tells me she might shack up with you now, but will find your beliefs (or lack thereof) repugnant down the line when the bud is off this rose. And then she will run back to mummy and daddy - like a child, not a grown woman.
Nah...I know it's been 18 months, but I think you're not asking enough questions. Never mind the parents and the ex. She sounds very...um...what is it?...immature? Perhaps you are rushing things - rushing isn't just about endurance and time. It's also about seeing who else is out there and getting your feet wet in the dating thing again. Have you dated others? Do you find it hard to meet women so you've lasted 18 months in this crazy situation? Are you just really lonely and she's hung in there so this is The One?
Look, dude, you're an engineer. You're smart. You own your own home. You have a son. You're successful. But like most engineers, (and I know a few), you might not be as savvy about women as you are creep crack growth. You are saddling yourself with two stepkids, an ex-husband, and two parents - none of whom are cheer-leading for you and you're doing it all for her. But is she worth it? Look more closely at her. She is not self sufficient and she's not even raising her own kids. She's harnessed to her parents in an odd 17th century way. She's talking out of both sides of her mouth on this religion thing. I'd give this way more time to...simmer. And besides - you have a son. You can't screw this up - he's been through enough already with your wife's death. If this woman is so great, why aren't you talking about marrying her instead of shacking up? If she's not worth marrying, and she's not worth driving that far to date, why would you shack up and co-mingle your son's daily life with hers? I really hope this works out for you. I think you have a lot to offer someone and should give yourself a few more tries to find a situation that's more welcoming to you and your son. I'd start by getting a dog

I take the position that I do not tolerate toxic people in my life. Family or not.

I would suggest that you and your intended focus on your own relationship and her parents can get on board... or not. As for the Church censuring her... if that church is important enough to her she can be pro-active and go see the minister and deal with him directly. That cuts her parents and the X out of the mix. Better to pro-actively neuter that crowd than continue to tolerate their manipulative crap.

If her conversation with the minister does not result in a tenable situation .... there are countless Protestant alternatives that would welcome her.... and you.

All IMHO of course.