Yes, you can daisy chain to 3 additional keypads if required. The panel can be placed at the start or in the middle of the chain. You just terminate each end of the chain, so if the panel is in the middle, remove the RS485 resistor jumper from the panel and place a 680 Ohm resistor across A+B at each end. If the panel is at the end, leave the jumper fitted at the panel and fit a single 680 Ohm resistor across A+B at the last device in the chain. The resistors should be in the pack that comes with the panel.
Eg. Any combination of devices:
Panel (680R) -> RIO -> Keypad -> Keypad (680R).
or
Keypad (680R) -> Panel -> RIO -> Keypad (680R).