up your alley

1. What does "up your alley" mean?

2.
a)My older brother will defray all my expenses.
b)My older brother will pay all my expenses.
c)My older brother will cover all my expenses.

Do all these setences have the same meaning? I am curious to know if there is a difference in meaning between sentence a) and the rest two.

Thanks.

Something "right up your alley" is something in your particular area of interest or skill.