It should be possible. But it also depends on what 5K monitor do you have.
If you have
5K monitor with 5120x2880 resolution, then you will definitely need a Thunderbolt docking station (for connecting the 5K monitor) and a DisplayLink graphical adapter that you could connect to the docking station (for connecting the 4K monitor).
I work at i-tec Technologies, so I will let you know about our products.
You can use any of the following TB3 docking stations:
https://i-tec.pro/en/shop-window/?ca...=Thunderbolt-3
And either of the following graphical adapters:
https://i-tec.pro/en/produkt/u3dual4kdp-2/
https://i-tec.pro/en/produkt/u3dual4khdmi-2/
If you have a 5K monitor with 5120x1440 resolution then basically any docking station with DL-6950 chipset can be used.
https://i-tec.pro/en/produkt/cadual4kdockpd-2/
https://i-tec.pro/en/produkt/cadua4kdockpdl-2/
https://i-tec.pro/en/produkt/catriple4kdockpd-2/