Upgrading from 6300, what lens and body

Hi, currently I have a 6300 with the kit lens "16-50 F3,5-5,6 OSS", and tele lens "55-210 mm F4,5-6,3 OSS"

Im condidering getting a second body to reduce lens changes on the field, and to have the option to let a friend make photos with me using that second body.

I was considering getting a 6400, as its an upgrade and shares batteries and optics.

Sounds right?

I also want to complement my optics, what should I get?

I was considering a "18-135mm F3.5-5.6 OSS" and another "16-50 F3,5-5,6 OSS" for the second body.

Any changes and suggestions?

Ty