Yes, banks give an education loan on collateral that is already under another loan, be it a home loan or an education loan (could be for your sibling). How much you can get will depend on the current market value of the property, the pending amount to pay off the loan, the lender, you’re taking it from, and so on.
Scenario Your elder sister has taken an education loan for higher education by putting your parent's home as collateral security. She had taken a 50 lakhs collateral education loan 5 years ago and has paid off 40 lakhs towards her education loan.
Now again the question is, can banks provide you an education loan for your higher studies on the same property (Home)? Yes, banks can provide an education loan on such property.