I googled your tires to be ST ( special trailer) and those are calculated in their maximum load for lower speed of 65m/104km/h.
This is because of more deflection of tire allowed at lower speed.
If you want to give these tires a deflection at wich a livetime of 6 years or longer , you should calculate with a lower maximum load .
And if you do so these tires maximum load will be about 15% lower.
Then the 4 tires can bare yust enaugh for your trailer.
I am known for hyjacking topics and dont want that, so I wil give the link to topic I started today in wich I will also add this ST story in time.
how to compare tires for replacement