Also how many people know we're here exactly? I'm not clear on that. Is it just the boss and some guards or is Janken going to be hunting us down?
Not necessarily. While it's clear that Doppel was tailing us from the start (possibly using magic, so
of course we haven't noticed anything), that doesn't mean that Janken will come down personally.
For one thing - judging by source material - he really like to indulge in '
Orcus On His Throne' behaviour. Satan directly challenged his might, but this? He is likely dismiss it as beneath his notice. Heck, in his very own game he didn't do anything about death of his most important minions, opting for Kidd to come to him instead! Quite a lazy bastard, that one. Our heft hides genuine
strength, unlike that blubbery choleric.
Second, while our robots are familiar with 'Pierrot', indicating her presence in the mansion for some time now, that doesn't mean Doppel Arle will alarm the Janken for sure.
Maybe she's disloyal (plausible, seeing his lack of care for wellbeing of his servants)? Maybe she a liaison from other faction like Rouge is for Eggman? Maybe she's straight up double-agent?
Heck, the whole battle might be a test to see if we are worthy enough to jump ship to, for what we know!