Thanks for your question. You do have Masonry bees. They are only active in the spring. Your right, they have now laid their eggs in preparation for next year. So you missed the boat for doing anything this year, as its August. Next year when you notice the very first activity, the bees emerging, flying about, THAT'S the time to act!
Try the The Hive Honey Shops Eco-Friendly 'Rehousing Method'
1) Make your plywood barrier habitat
Take a large piece of plywood 15mm thick, large enough to cover the entire area of the wall they are coming out of. Take a size 7 wood drill bit and drill lots of holes through the plywood sheet. Screw that to another piece of plywood the same size. Loosely refill the drilled holes will either sawdust or soil. As you have sandwiched another piece of plywood to the back of the one with drilled holes, the bees can enter the drilled holes only but no further. They will be unable to re-enter the fabric of your building.
2) Fix your plywood barrier habitat
Now around 8am on a sunny day when the bees are flying, screw your plywood to your bee infested wall area, holes facing outwards. As the bees are out flying they will come back to your plywood barrier. They will enter your drilled holes and lay their eggs in the plywood, not the wall of your building.
3) Remove & relocate your plywood barrier habitat
Once the bee population dwindles, about 1-2 months later, remove the plywood and place it in a far corner of your property. You have now successfully caught all the eggs for next year in your plywood habitat. Next year your bees will emerge from the plywood not your property wall.
4) Seal the holes in your property wall
After you have removed the plywood habitat, this is the time to properly seal the holes in your property wall. Use concrete if the holes are in the pointing, fill as normal. Unless you fill them properly you will have the same problem year after year as the masonry bees will reuse the holes again and again.
The nice thing about using our plywood method is that you do not harm or upset the bees and you do not disturb their natural life cycle, just alter the location where they breed.