If grandma doesn't already know, I can't wait until grandpa comes to visit, takes a good look at that baby after seeing many pictures, notices how she acts around her daughter and goes "We need to take this DNA test RIGHT NOW, Kako. What if you're not the father? It could be a scam just because the child looks like you" since, idk, men might have more fear of the scenario of suddenly having a woman with a young child you never met knocking at your door and saying it's yours too since it only happens to them (FOR NOW).
Once it's confirmed the child is hers, dad can say "You're gonna have to marry her now, you had gotten her pregnant" and suddenly Mirai becomes besties with her father-in-law for speed running her seduction plan.
Point is, I need the parents to suspect and be ok with it in a single chapter so we can have all of Kako's family and friends rooting for her to marry the baby mamma.