aabha_in_us:

 regardig your secondary concern (I am more concerned bcz my parents can not read and write english. They can not communicate if they do get any problem.)  as long as they can manage a bit of Hindi they should be fine because in my experience, which is at least 3 times a week (dont ask my what I do, But I don't wear a name tag on my shirt), Hindi (including Punjabi and Gujrati) is Heathrow's second business language after English.

Hope this helps.

_x