I have not done much QAYG but if it were mine, I would probably appliqué the owls first. Now because it has sashing anyway, how about quilting them in strips, assemble 5 rows sandwich and quilt seperalty, then attach together with your sashing, then the boarders can be added with batting and backing. I think it's very doable, since the blocks all have sashing anyway. Others may have better instructions for this technique or maybe there it a tutorial here