My general opinion is that if you are worried about having personal information on a device that is prone to theft – don’t do it.
Groups cannot be password protected. But even if you could, If you are have a password on DTTG, why add another layer – it’s not going to make things better.
BTW, if you are stuffing your banking info onto your iPad/iPhone, then make sure you have configured your iPad to wipe its data after a certain number of passcode attempts, have long passcode rather than a short one, and use Find My iPhone to wipe your device if its lost.