Feelings don't require validation; they just are what they are. And they are our own business, not anybody else's. So, your feelings about your in-laws, including your anxiety about their judgments during your pregnancy, are valid for you, and they are nobody else's business. In exactly the same light, your in-laws feelings about you and degree of excitement about your baby are valid for them, and they are not your business.
That's not quite the end of it, though. Because our thoughts, what we decide to dwell on, or how we interpret a situation, help determine what feelings we're going to have. That's still our own business, but there are always choices, so there's at least a possibility shifting it toward feelings that are less uncomfortable.
So, if you would prefer your feelings toward your in-laws to be painful (you might want to consider whether there's a payoff for doing that), then you can continue to focus on their disapproval of your first pregnancy, and their seemingly greater excitement about another grandchild.
However, if you'd prefer to have good emotional connections with your fiance's family (and there are some terrific possible payoffs for that), then it's up to you to decide what thoughts you want to focus on. Comparisons and resentment are killers of joy and love, so you might usefully put your attention on whatever positives you can establish.
Because of your sketchy past relationship, you may have to work at this, but in my experience, there's often something good worth building. You have kept your distance, for reasons that seemed good to you, but now that the fruit of those reasons isn't so sweet, you might want to explore what happens if you keep your heart open toward your in-laws. It sounds like you are definitely planning to make them family, if you haven't tied the knot already.
One other thought – as a woman in my 60's, I have seen that age does not necessarily make a person more mature, wise, or compassionate. (Notice, for example, how your MIL projected her judgments about her own out-of-wedlock pregnancy onto you. Sounds like she's really stuck.)
So don't wait for your MIL to reach out to you. She may never have learned that she has that option within reach. But she may be surprised and responsive if you reach out to her. Do you have the maturity to give that a try? If it turns out that a relationship with your in-laws is not positive and nourishing for you or your child, you can always choose to increase the distance between you again.