Check the specs on the trailer. It will show the weight ratings of the axles. The tires should have at least the same rating as the GAWR of the axles. I like to have at least 20% extra tire weight carrying capacity above GAWR. Mine are at 45% above GAWR now.
The Goodyear Marathon ST trailer tire listings I found at Tire Rack only go up to E load rating at 3420 lbs. each at 80 psi. So a pair would be rated at 6840 lbs.
https://www.tirerack.com/tires/tires.jsp?tireMake=Goodyear&tireModel=Marathon+RadialI'm guessing yours has 7000 lb. or 8000 lb. axles. A Goodyear LT235/85R-16 L.R. G is rated for 3750 lbs. at 110 psi, so it's rated for 7500 per axle. That's the highest rating I could find for a 16" Goodyear tire.
http://www.goodyearrvtires.com/pdfs/rv_inflation.pdfAxles are typically rated at
3500
6000
7000
8000
10000