Can American friends work there through tourist visas? How long can I go? Is it okay to practice there? Will this side admit it?

If you want to work, you must change your work visa.

A work visa is a visa with a work contract time given by your foreign company.

Internship is certainly possible.

As long as there is evidence, this side will admit it.

But the important thing is. ..

You can't work regularly on a tourist visa. ..

I don't know whether your work can be completed accordingly.

But you can get a lawyer to transfer your visa. ..

If that company is willing to transfer your contract. ...