Meike MK-Z-AF1 11mm and 18mm Extension Tubes for Nikon Z

Yes they will with Nikon Z mount lenses.

This will mount to and should work with all RF-mount lenses. Overall functionality (focus distance, autofocus speed, etc.) will vary from lens to lens.

Teleconverters and extension tubes have different usages and are not often used simultaneously. A teleconverter is is designed to increase the focal length of a lens by the multiplication factor listed on the teleconverter, giving you additional reach to your subject. Extension tubes are designed for macro photography, and are designed to reduce the minimum focus distance of your lens while increasing magnification, and also eliminate the ability to focus at infinity or use the lens for normal shooting. Hypothetically, using a teleconverter and an extension tube simultaneously with a telephoto lens would reduce the lens' would allow you to focus closer than the lens' listed 2.95 feet (90 cm) minimum focus distance, and would also prevent you from focusing at infinity, essentially making it a long macro lens. Unfortunately, as this is an unorthodox setup, and as the Canon Extender RF 1.4x and the Canon Extender RF 2x is designed to connect directly to the lens (the optical element on the teleconverter is designed to sit inside the rear of the lens for optimum optical performance), I cannot state if the setup you describe would work, nor if the lens would focus properly with the teleconverter's optical element out of its designed alignment inside the lens, and this would not be something we could test.

Can these work on a Z50?

No, these tubes are not weather sealed.

Caps - yes; case - no.

Yes, an EF lens on the R adapter will work with these extension tubes with full electronic communication.

It depends on the original lens you are using these extension tubes with. If you are using a lens that is 100mm with 1x magnification and you add 29mm of extension tube to it, the magnification will become 1.29x.