Yes in another country five years apart-I didn't meet the older brother till my second visit.

Not exactly the same, but:
I dated a guy for 6+ years. His family loved me. We ended up breaking up, but stayed friends.

Later on, his sister and her husband (ex's brother-in-law) were trying an open marriage, and I ended up dating the husband/brother-in-law. It was fantastic... for a little while. I loved being back as part of the family; their kids/ex's nieces and nephew are amazing. I think their mom was really happy about it, too.

Unfortunately, the whole situation ended up falling apart because the sister's/brother-in-law's foray into an open relationship was... not that great, because of some other drama (like, whooooaaa) -- it's those other aspects that soured the situation.

On the plus side though? The sister's partner during that time period is now my current partner, and we are going to celebrate our one-year anniversary in the next month or so (fuzzy details, lol). And, despite technically knowing each other for a long time (we met when I was dating the first guy), we never really talked before then.

Not exactly the same as the question situation, because of the "in-law-" and the ethical non-monogamy/polyamorous aspects, but...

nope . souneds sexy