Can guests who scanned the table QR code split the bill themselves on their phones?

No. A guest who orders from the QR code on the table pays the way you set for dine in, and any splitting is done by staff on the POS. Open the table, press Split the bill, and split by item into up to twelve bills or evenly up to twenty ways. Two guests can also scan the same code and each place their own order, which lands on the same table. The Tables, tabs and the kitchen screen tab in the docs has a guide on splitting a bill.