Should I merge my Brave Ikes?

Save for Steady breath, this skill is too good to even consider merging so you'd better pass this over to someone like Black Knight. I think his native B slot skill is fine as is, Beorc's blessing is exclusive to only him and it's good.

Use it for Black Knight, Lukas, or Dragons. They benefit a lot from having a skill like that. The other option is to save it for any future units that might also use it as well the the aforementioned. Definitely don’t merge a good fodder like Brave Ike.

As for QR2, I don’t think it’s worth it personally as it works against his Aether CD timing, but if you’re running Bonfire then it’s definitely his best B-Slot.
I would actually use Beorc for Arena, Guard for Dueling, and Vantage as a safety net option.

Hope this helps.

I'd Highly recommend keeping the extra's for future units, if you don't have units who can make good use of them already.

Steady breath is an amazing skill and makes some units break through into much stronger ones.

Units mentioned below are really good candidates (BK, Lukas, Nowi, Y!tiki, etc).

The benefit you get from merging is 1 additional HP and Atk stat for B! ike, which is kinda marginal.
While the benefit a unit can get from Steady breath is much more noticeable.