Sketch looks great- everything is very clear and detailed

I must admit I would go for area that can only be reached by crawling(it's just a matter of adding a small obstacle/wall with small opening). The different buttons that indicate which player should operate them could over-simplify things, and we are going for partly realistic surroundings. But we could make some sort of help-option were the buttons & other things could be lighted in manner that explains which player should do what/or what must be activated in order to finish level.