Swallows nesting in garage

I am about to move into a new build property and when I visited the site the builders had left the garage door open and swallows have nested. They have said we can’t  move the nest and need to give the parents access to the nest. However, that will mean the garage is open, not secure and we’ll have many thousands of pounds of bikes, tools and garden equipment in there at risk of being stolen. This is a very big issue for us but with contracts signed we’re now committed to moving in a few days. Any suggestions on what can be done?