since no one answered, I will give it a shot.
for the shrugs, I feel it most when I shrug up while pushing my shoulders back as if trying to get my shoulder blades to touch. At the bottom I push my shoulders as low as I can to get better rang of motion. I just started doing DB shrugs seated while leaning a little forward and it has been great so far. However, I see many doing it the same way you are, so go by how it feels and the mirror. The weight appeards too heavy in the video but that could be your range of motion.
for the DB press, it was hard to tell but it looks like your elbows are too far to the front? other than that, it looks good.