As someone who works in a doggie daycare and has witnessed all sorts of play styles... this looks totally normal. Even my boys do it, one more than the other.
I would discourage allowing the cocker spaniel pup to take food from your sheltie though, as well as try and introduce lots of time to them separately/away from each other. They're both young and need to learn coping skill by themselves and learn not to rely on each other too much.
Cosmo - Blue Merle Boy - 2 years old
Jet - Tricolour Boy - 2 years old