It's just as related as the 3 American black widows or the European one are to each other, they are all species in Latrodectus. And while most Aussies do call them redbacks calling them Australian black widow isn't unheard off, especially by non-Aussies.
It's the term "black widow" that's ambigious here, it doesn't refere to one specific species of spider.
How many Widows we talking here? They’re common, but if you can see 10+ in one garage that sounds like an infestation you want dealt with professionally.
Sounds like you had a recent hatch in your garage. This is time of year for it.
It depends on your risk tolerance. If you have a lot of stuff in your garage that you need to access, I’d probably call a professional.
It there aren’t many hiding places for them, I would just vacuum up the ones that I would likely come into contact with.
I might call a professional. Unfortunately, with our garage, the ceiling is unfinished, which means it has open rafters and plenty of places for them to lay eggs. The tallest point of the ceiling is as high as the roof.
There are some at ground level when I walk out into the garage. Is it possible to vacuum them up? I really don’t want to touch them, or bat at them with a broom. I feel like if I do that, they’ll hit the ground and charge at me, or crawl up the broom.
You can vacuum them and it probably won't kill them initially but as long as the chamber is relatively secure (doesn't have to be airtight just no obvious way out), they'll eventually perish via starvation or asphyxiation. I understand that spiders "breathe" through their skin and enough dust can clog that up. Just be prepared not to empty that chamber until you can confirm they're dead.