How to let my dad and me and my brother go to the mall?

Ok so both my dad and my stepmom work during the day but one (my stepmom) works at macy's at the mall. me and my brother (step) are both responsible. hes 14 (sice mid-march) and i will be in a month. Me and him both watch my little sister (half sister, 3 yrs old) by ourselves from 10-10 with no problems. He let me walk to tacobell with my little sister before and its 3 blocks away (plus we dont exactly live in the best neighborhood) and we would take the bus AND my brother has taken the bus to school by himself and school is farther away than the mall. My brother knows the correct buses and everything so I don't see why he won't let me and my brother go there. He wants to check out the lego store, my little sister like sto ride the kiddie rides and I want to look in victoria's secret because I need some new bras and I'm gonna find out which ones I like and the my mom (real mom, my parents are divorced) is gonna by them for me online. How can I have him let me and my brother go to the mall with my little sister on the bus?