Lose the pad on the bar. It might feel uncomfortable at first to have the bar there but it is much more stable and in time will actually be more comfortable than with the pad.
You are trying to do high bar squats yes? Because you are performing much more a low bar style. You aren't getting to parallel and you are not remaining upright enough. You need to shove your knees out harder and sling your torso in between your legs. Keep the weight on the heels. Also keep the chest up, tense all the muscles of the upper back and squeeze the bar hard. Everything must remain very tight.
Thats IF you are trying to do HBBS. If you want to do low bar you need to put the bar in the correct position on the back.
Your mate is getting nowhere close to depth. He needs to get some more suitable shoes also.