Fayne answered the first question while Nattorei already answered the second, but I'll elaborate upon the latter.
First Camilla, her ability is in between Liana and Iris' ability in power, a 700 HP heal upon deployment to all units except those unable to be healed. Her Awakening Skill is an inverted version of Iris', she starts at 1.6 power for the first usage, but raises to 1.9 for the second, and 2.2 for the third and beyond usage. So she rewards liberal usage of the Awakening Skill. Now, out of your healers, your three best candidates are Liana, Camilla, and Chydis; Camilla fills the same roll as Iris, but performs better. Right now Liana will be more niche with raw power essentially on par with Chydis, but with a superior ability and a fairly nice Awakening Skill as well as being able to do a few tricks with range. Camilla will have the best burst healing and will reward using her skill with her Skill Awakening, but will have the lowest raw healing out of those three with a middling ability when compared to Liana. Chydis has the worst ability due to her low HP, raw power roughly on par with Liana, and the best sustained healing with her base Skill and Awakening Skill. So, you have three good options depending upon what you want out of your healer or who you prefer out of those three.
Now Sasha, she has a great deal of raw power, even without the 7% boost from Garania's ability she surpasses Awakened Garania benefiting from her own ability in raw power, not to mention the attack speed boost she possesses which will further increase her DPS. So, if you only deploy a single mage most of the time, Sasha would be a better option to awaken. However, if you deploy more than one mage most of the time, Garania may be a better option since she's a force multiplier and would strengthen all of your mages. They don't have Awakening Skills yet, so I can't give any analysis on that, so there's no telling how they may compare once that is released.
