yes, definitely!! If you and your sister are not earning on your own and are not married, then you can definitely get a certificate for Economically Weaker Section or EWS under your father if he fulfils the required norms for the same like income less that 5LPA, land less than a certain amount and so on.

So, in general, if you are not earning and are unmarried then you can apply for EWS certificate under your father. Hope I have answered your question. All the best!