On sumos: I cannot see your foot position, so I can't comment on knee alignment. I hope all is well there.
Focus on getting up with your shoulders and butt at the same time. Right now you have two stages:you get up with your butt and your back completes the move. Since I don't have a video of me doing sumos, here is a side DL,but you can see how shoulders and butt move together. Hope this makes sense.
http://spidersport.com/side-deadlift.php