Price Sets for different groups
Do you mean this extension:
https://github.com/zengenuity/civicrm_groupprice/blob/master/info.xml

It's info.xml says it's compatible w/ 4.4 - I think that explains why you're having difficulty to get it to work on a 4.7.x 

If this functionality is very important to you - the general guideline is:


contact the author of the extension
check with them on possible plans for an upgrade of the extension to a newer civicrm version
and what kind of funding it may take to get it there