Jinx has poor laning and Janna is meant as a passive support for disengage. Ashe has longer range and better harass. Unless you're more skilled, you'd be better off focusing mainly on farm and only poke with Fishbones when safe and have mana to spare. It matches Ashe's auto-range at rank 1 and begins outranging her with more ranks. Jinx is a hyper carry, her strength lies later in the match and she'll outscale Ashe hard.
As for Sona vs Janna... Sona used to be seen as a counter back in season 3. Technically, a sustain support counters disengage supports, but Sona has been nerfed so hard on July 30th that the matchup becomes extremely questionable. Sona has less damage, less mitigation, less mobility and less CC, but still has higher AA range and a heal, albeit the shittiest and most expensive heal in the entire game. Optimistically, I'd call this a skill match-up, but Janna is incomparably more valuable to her team as a whole. Assuming the ADCs were on-par, the Janna side has the 2v2 advantage.