What an excellent and satisfying backstory for Molly. It adds some lovely depth and context for her character — when you think about her losing family in the first war, and losing a healthy relationship with her parents on top of that, it puts her protectiveness toward her own children in a new light. And it makes complete sense to me that the pureblood world would pressure a young woman to live the life they want for her, but it's rare for authors to consider how that affects the "good guys", not just the Slytherins.
Arthur is great in this too. His concern for being able to provide for Molly seems very in-character, and I like how clear you've made the love between them. She doesn't choose him to get away from her parents, or to get away from her stifling life (though those would have been reasonable motivations), but because of who he is. He understands her, and that's what she needs the most.