Yes, these devices will work. The AC3000 is tri-band, which includes one 2.4GHz band and two - 5GHz bands (one for device connections, and one dedicated for router-to-router communications). The Orbi makes it simple and automatically connects to your devices based on the best available network option, which in your case would be the 2.4GHz network.
I've read reviews where people state that their 2.4 devices aren't connecting properly, but I think those issues are isolated. And through the Orbi app you can turn off the 5GHz band, so that is a good way to trouble shoot those kinds of issues.
I hope this helps!
Scott