You don't tell them to get off, you ask to work in.
It's sharing man. You're not saying "This is mine now, no one else can use it until I'm done", you're asking "Can I use that piece of equipment to?"
You gotta keep in mind, you all paid to use the same equipment. You're all equally entitled to it. That means that, when multiple people want to use it, you just gotta share it.
I've worked in with groups before with no issue, and let groups work in with me as well. It used to just be a thing you did when you went to a gym. As our culture has grown increasingly passive aggressive while our interpersonal skills have rapidly diminished, the notion has essentially vanished.