Black & tan dog-
Face: ears loose but slightly back, eyes and brows soft (not wide, squinty or tense), no facial ridges or wrinkled around his mouth (which if present, would imply tension or heavy breathing)
Head: raised, not looking directly at the other dog
Tail: can't see
Body: in motion, slightly forward leaning with one leg loosely outstretched
Brown & white adolescent puppy-
Face: ears raised and pulled forward, eyes slightly wide and brows slightly raised (alert, interested), mouth open with relaxed lips and tongue pulled back
Head: lowered slightly to the height of the other dog, directly gazing at her interest
Tail: loosely raised and angled (in motion)
Body: also in motion without tension, but hind legs are pointing slightly differently than front legs, implying a change in direction
Please review the above body parts and compare with the photo to spot these cues yourself before read
These are my dogs a few years ago, in my backyard. At this point they knew each other well and had established a good relationship.
This one might be a bit tricky! In the dog world, seeing side eye or the white of dogs' eyes (sometimes called "whale eye" or half moon eyes) usually rings alarm bells. But it's important to look at more than just those whites. Truly upset facial expressions contain lots of tension, and half moon eyes are typically called such because they're wide and rounded. A dog who is interested or alert and avoiding direct eye contact though, will show that expression even when not upset. In the above photo, we see a clear lack of facial or body tension in either dog. The black and tan dog may be avoiding eye contact and putting ears slightly back because he's just barely annoyed, maybe he doesn't want to get run into, or perhaps because he knows the other pup wants his ball and doesn't want to move it closer to her by turning his head. It's tough to say since we can't read minds and that's okay. Regardless of the reason, there's nothing to worry about here.
The brown and white pup on the other hand is more transparent. She wants to play and/or she wants the ball. Knowing her, it was probably both! I do note her slightly lowered head which implies peaceful intent or conflict avoidance, as well as her tongue being pulled back. The latter could be coincidence, but could also mean she's preparing to grab the ball or mouth the other dog. Again knowing her, both are common. Either way, if pulling her tongue back was intentional vs letting it flop out, it makes sense she wouldn't want to get her tongue caught in her teeth.