PLz help me there are many Q's i have to ask plz ans them?

I have a Friend with who i hangout he is 1year older than me but it doesn't matter he has a sis hu i think who likes me the thing is she looks at me like most o the time n tried to join our talk........i kinda like her n wanna date her her bro is cool with people dating her but i dont knw how to ask him so plz help........1 does she like me????.....................2 plz tel me how 2 ask her bro to b cool with it?