Japanese are usually quite strictly following the rules. Some hotels even charge difference based on single or double occupancy and likely to charge anything beyond.
I had a quick look and at Hyatt, I would suggest Hyatt Regency Osaka Tatami Suite, which seems to accommodate 5 adults. RC Osaka has Tatami Suites as well. Hyatt might give breakfast/lounge also for 4 out of 5 (2 adults + 2 kids) vs Hilton or Marriott who are just member +1 policy.