@thegoatrider Well, let's remember that ever since he returned to Earth, and through all the brouhaha that's happened so far, I reckon it's been less than a week. In fact, since the moment Sei'ichi entered the mansion, just a few hours have passed. And before that, it was looking for the way to Souboutei, exorcising his former home and meeting the Prime Minister. So he hasn't talked about his brother because he hasn't had the time.
Which, come to think of it, means that time is still distorted inside Souboutei. One week has passed for the survivors outside, but inside, it has been fighting non-stop, without time to rest, eat or go to the toilet. As Zanka and Kaerikuro said, for them it's been just a few hours since entering, and yet 80 years have elapsed.