Dusty Hill is a real bummer, I grew up listening to ZZ Top on the radio all the time. In particular, while Gibbons does most of the vocals, Dusty Hill was a solid singer himself, in particular Tush maybe could be his most well known song he was lead on and is a great tune. He will certainly be missed.
Joey was a surprise just because he was only in his 40's, which real rough. It's sad he never got to seemingly sort things out with Slipknot, do some stuff with them again.
Another to add to this was Mike Howe, he was singer for Metal Church in the 90's and then reunited with them in the 2010's. I don't know him as much from that stuff, I listened more to their first two albums and their 2000's output, but I listened to some of the stuff from the 2010's and its a bummer for him to have passed after only having reunited a few years back.