House sparrows nesting in my mortar/bricks

Hello, I hope someone can advise me. I've noticed on one of our external brick walls, there are quite a few holes in the mortar and it seems like there are house sparrows nesting in there. First, will this cause further damage to the house, eg, leaking when it rains etc? Second, if I wanted to repair the mortar, what time of year is safe to do this so that I don't disturb any nesting activities?

I don't really want to turf the birds out, but also don't want our walls leaking - if this doesn't cause problems I'll happily just leave them in there.

Thanks