https://fireemblem.gamepress.gg/fire-emblem-heroes-iv-calculator
Some of your characters are Level 1, so you can check the IVs on them easily. Meanwhile, any 4* or lower characters you've gotten a level for need to wait until 20, then check Unlock Potential, then look at the next stars starting stats. Brave Lyn, Ike and Fjorm are Neutral IVs, since you got them from Free stuff.
Looking at your Heroes, you have some decent characters for your Blessings. Basically, for getting Ike and Fjorm, you've gotten a Earth and Water Blessing respectively. Blessings give a boost to characters when the respective element is affecting a day(shown in the top-left corner) and when a respective Legendary Her(like Vanguard Ike and Fjorm) are on the field with them.
Blessings gives you an HP boost as well as a boost depending on the hero on the field. If Fjorm in on the field with a Water Blessed Hero, they'll get HP+3 and Speed+3. If Vanguard Ike is on the field with an Earth Blessed Hero, they get HP+3 and Attack+2.
So basically, you want to choose characters that can use the Blessing to good affect and is a good teammate for the Legendary Hero. Like you don't want to choose another Lance to go with Fjorm, since that would be 2 Lance characters and less Triangle Advantage coverage. For Ike, a Sword character wouldn't be a good choice for a Earth Blessing right now.
Okay, now for choosing Blessings for your Heroes. For one, Brave Lyn is already a good pick for a Blessing and she can appreciate both the Attack and Speed boost. However, you can only apply 1 Blessing to a Hero, so Lyn can only have either the Water Blessing or the Earth Blessing.
For your non-Lyn characters, all of your characters, except your Staff user Wrys, can use the Earth Blessing well. However, it's preferable to choose one that can go well with Ike. Anna and Hawkeye can work well, as they both have great Resistance and can deal with Blue Mages that endanger Ike. Otherwise, any other character is personal preference, although it's preferable not to use another Red to go with Ike.
For the Water Blessing, it's a bit tougher. If you don't give the Water Blessing to Lyn, Tharja and Soleil are your best picks for the Water Blessing. They both like the Speed boost as it helps them double and be doubled by enemies less. They both can also be protected by Fjorm once Fjorm gets Reposition from a Barst or Selena.
Either way, considering you're new, I suggest giving Lyn one of the Blessings. She likes either of them, so it's up to you to decide whether you want her to have more Attack or Speed. But know that the Blessings' stats won't come up if the Day(in the Top-Left corner) is not attuned to the Blessing. Might be best to do a Water Blessing as next month should be a Water month.