If you use Google Messages you can do that for texts (you may have to use the web interface, though... not sure if the Messages app itself on another phone lets you sign into your account or can only support the phone itself). However, for calls, the 'Call and text from other devices' option is only available between Samsung Tablets, Computers, and Watches with only one phone as the 'main' device supported.
You can forward calls using the 'native' TMobile service, but for texts you'd have to either use Messages (and cloud sync with your Google account) or a 3rd party automation app like Taskr where you can set up a routine that automatically copies and re-sends any text you get on one device to another.