There isn't much to worry about, honestly. 82-year-old Stanley Weston "created the original idea of manufacturing and selling male action figures wearing and carrying miniaturized versions of the uniforms, insignias, emblems and equipment of each of the different branches of the United States armed forces."
This is the same kind of shenaniganry Jack Kirby's heirs have tried against Marvel, and the Seigels and Shusters tried against DC. And in fact, just last year someone tried to "reclaim" the MotU rights from Mattel. None of the efforts have worked.
Weston pitched his amazingly original idea - which, remember, was "dress toys like soldiers" - to Hasbro's Don Levine. The idea to have articulated figures came from Larry Reiner at Ideal Toys, and the actual design of the toy was done by Hasbro employee Sam Speers. If you believe Weston, Hasbro did all this work on his behalf, instead of the other way around. He offered to pay for the prototypes, but Levine told him that would be covered in the sale of the rights.
The name "GI Joe" was long used as a generic term for infantrymen, and even turned up in the movies as early as 1945 - decades before the toy. The characters were created in the '80s, by the one and only Larry Hama. So basically, the only thing Stanley Weston could really lay claim to is the very idea of soldier toys, which is nothing new. In short, you probably don't have anything to worry about.