Once you're in control, select you first party member. Play multiple times to see what everyone has to offer!
After making your first selection, head right and grab the crowbar.
Head left of the characters and use the crowbar to break away the boards. Hang onto the crowbar for now.
Setting foot inside registers the current character as a party member. Select your other two members.
Follow the path until you drop down. Head right to find this crate.
Drag the crate far left, and use it to hop onto the high ledge.
Stand all three party members on the bridge to break through and drop further into the cave.