hi,

yes you may use the ews certificate for all government jobs and admission in all india. right now in india only the state government are issuing the ews certificate. the annual income limit has been set by the central government for admission to central government-owned colleges and jobs offered by the central government. so if it matched with the state government criteria than you can surely apply through it. in general  ews certificate is not only based on family income but also the property owned by the family. if  family income is less than 8 lakhs but  they have the following property they are not eligible for ews category,

Five acres agricultural land or more

Residential flat of 1,000 square feet or more

Residential plot of 100 square yards or more in notified municipalities

Residential plot of 200 square yards or above in areas other than the notified municipalities