As for the whole unmarried sahm judgement, she didn't ask this, she's been accused of not understanding how it works and having a chip on her shoulder, you have no idea of her situation. I'm a sahm, 2 kids, not going back to work, not getting married queue outcry of horror, my house is in my name, no mortgage, I have my own money that I earnt before the relationship, to get married I'd be the mug, you know nothing of her situation, who the house belongs to, who the main earner is when she returns to work, if she has money for another source, absolutely none of your business as its not what she asked.
Op ignore it, appears to come from a place of jealousy that someones got 5 kids, happy and still getting it on.
The OP could easily and politely just reply that marriage isn’t in her best interests but thanks for the concern. Better that than people don’t give well intentioned warnings to someone who may really need them.
Of course I could be wrong but given the OP has five kids by 30, the first at 17 apparently, I’m willing to bet that it’s unlikely (albeit not impossible) that she has a solid career and pension behind her or that she owns their home outright. In which case, your situation (great as it is) would be entirely unrelated to hers and your well-intentioned reassurance could be very damaging.
And I for one am absolutely not jealous of someone with five kids! Good on her but really, do we have to accuse everyone who points out some potentially questionable issues ‘jealous’. This isn’t the school playground.