Given how long Kyoko has enjoyed seeing Kaoruko be a regular at their shop, I think Kaoruko's overly worried about winning Rintaro's parents' approval. I'm more concerned about Rintaro winning HER parents' approval... we barely know anything about what her family is like.
Man I love how confidently Kaoruko said it to Kyoko, so direct and to the point, as if she was also excited to declare it herself. I feel like Kyoko actually physically aged from her smile after hearing that... I can just imagine her inner thoughts after hearing her: "Oh, my little boy really has a girlfriend now... guess it's only a matter of time until she becomes my daughter-in-law and I meet my grandkids"
I'm guessing his dad will at least show up for a bit after the ladies' talk. Rintaro did say he wanted both his parents to meet her.