What is the ruling on a brother looking at his sister if she is wearing very tight clothes at home and does not observe proper modesty?

"Girls should not appear in clothes that describe the 'awrah (private parts) and cause temptation in front of their brothers, because this may lead to serious consequences. Brothers, in turn, should lower their gaze from anything that arouses desire and invites temptation. Scholars have agreed on the prohibition of looking at a non-mahram woman (one whom a man can marry) and mahram relatives (those whom a man cannot marry) with desire."