International law for inheritance

that is really not going to work at all, since the policies under which your cousin was coverd are governed by US laws,besides depends upon the niominations made by your cousin; however you can approach socailly legally it will be wastage of time and funds. 

1. Your Cousin's parents can claim EQUAL share in the properties located in India, BUT will not be able to claim any share for any proceeds received by Cousin's Wife under USA laws, by filing proceedings in Indian Courts or thru USA courts, more so specifically since Cousin was a USA citizen and not an Indian Citizen.

Keep Smiling .... Hemant Agarwal
VISIT: www.chshelpforum.com

Whether your Cousin passed away in-testate? If he had left a Will, and in that Will, he left any of his estates to his parents, it is possible. Otherwise, it is a long shot and the attempt itself takes decades, which due to the efflux of time is a waste of time, money and effort.  The only way is through a family settlement where the elders can prevail upon the wife of the deceased to spare some amount to her inlaws.

As per Indian laws parents have an equal share in the estate / claim of their deceased son, which may differ in US. 

It is better to settle the issue amicably.

It is advisable to consult and engage a prudent lawyer having expertise with Indian and US laws on the subject with relevant document for appreciation of facts, professional guidance and necessary proceeding