Seliph is kind of weird... His default skills all depend on him being below 50% HP, like Tyrfing's +4 Def, and Brash Assault. I'm working on a build for him that involves Defiant Def in his A slot, so as long as he's below half HP he can literally ignore every axe user in the game up to and including +Atk Hector or Cherche... but if any mages so much as fart in his general direction, he'll probably die. And he doesn't benefit much from any other buffs except Spur Def. When Sigurd comes along, on the other hand, and can enjoy the full set of cavalry buffs... Then again I'll probably be tempted to just run the Silver Sword+ on Sigurd, in honour of the Silver Sword he gets in the prologue of FE4 that makes him the most overpowered unit in the whole series (even Seth doesn't stand up to him, if you ask me).
I also had one pull on the Tempest Trials banner, and landed Ephraim and Linde. They're not who I wanted either, but I don't believe I can complain too much.
Thinking about stacking Breath of Life on Linde to make her a healer for the Trials - 15 HP healing every time she attacks sounds pretty handy to me. While Ephraim can eat reds for breakfast with Triangle Adept and Quick Riposte. I at least have a 4* Mae I pulled a while ago, so if I don't get her trained up in time the plan is to just send her out on her own as team 1 and surrender straight away, and hope I can get through the whole thing with only three teams.