Is it possible to connect two 4k monitors to one thunderbolt port?
What you want to do is possible, but not without either using an adapter, dock, or the right kind of displays. For example:


you can use a display that allows you to daisy-chain to another display (i.e. you have a charger plugged into one of your ports, and you have one display connected to the other port and a second display connected to the first display)
you purchase a dock such as the OWC's Thunderbolt 3 Dock.
you purchase at least one display that will provide charging power to your MBP (e.g. the LG UltraFine 4K Display).


You may want to also read:


About Thunderbolt ports and displays
Connect with Thunderbolt 3 on your new MacBook Pro
Use the LG UltraFine 4K Display with your Mac


NOTE: IMHO, if you're wanting to run two 4K displays you probably should invest in a MBP with four Thunderbolt ports, as this is likely to provide more flexibility in terms of usage and the variety of devices you can purchase to meet your needs.