Straight Talk isn't a carrier, they're an MVNO (mobile virtual network operator). They use all 4 of the big carriers, so one phone may be on a carrier that allows hotspot usage, the other one may be on a carrier that doesn't. (If you bought the phones in Straight Talk boxes, the color of the map will tell you the carrier it's on.)
And lots of luck talking to Straight Talk. (You'll probably get better results on their Facebook page.)