Hello all! This is my first post and not really a question as much as a request for experiences and reassurance.
My 13-week old puppy, Hades, and I live with my mom. Just 2 days ago, my older sister moved back home ("emergency" situation) with her 1-year old Miniature Schnauzer, Max. Since then, Hades shows little interest in me beside feeding times and short tug sessions.

Of course, I know it is natural for him to be intensely interested in another dog. However, he won't even come lie down in my/our room anymore. He will sleep by the gate separating the two dogs and perk up anytime my sister or Max move. Max is like velcro with my sister and Hades, so far, has been more independent with me in exploring the world. With Max following my sister everywhere and Hades wanting to follow Max, I am worried he will begin to see her as his "leader" and not me. He still follows my commands, still noticeably enjoys our training sessions before feeding time, and still comes to me to take him outside. Again, it's only been 2 days but I want to know how to prevent any negative changes (for me) before they happen.
Max is a reactive dog. If they are separated by a gate, he will snarl furiously and growl at Hades. If I walk up to the house, he will bark and growl right up against my leg until my sister grabs him. He has pretty strong separation anxiety as well. If they are outside, the only thing they do is "play fight"
nonstop. Max is only the 3rd dog Hades has met. With the other, older, calmer dogs, Hades was playful but neither dog did any play-fighting. With Max, Hades is constantly on his back and they are mouth-biting, jumping on each other, etc. Hades keeps coming back for more so I can only assume he's fine with it. I normally would not have a problem with a bit of play-fighting but this is really constant. From reading threads on here, I guess some dogs just don't get along as nice??
As Hades is only on his 2nd set of shots (backyard breeder), I can't take him for walks or to the puppy class I want to sign up for (Big Basin in Modesto, CA). I am hoping that, over time, Hades will grow desensitized to Max's presence and more interested in spending time with me. I will be able to take him to puppy classes at the end of the month. In the meantime, what can I do to make sure Hades stays attached to me? I am taking him to Starbucks, Lowe's, and hanging outside Costco tomorrow morning for people socialization. Should I up the 1-on-1 play/training time at home?