Sad to hear that...
But still, as the eldest, you need to set an example for the
young...
No matter how much you think they won't follow, you can still
influence them a little...
For the bike part... i guess you need to wait a little longer...
As, it is not as cheap as you think...
And help your mum a little...
Even if you can't help much with financial, you can help them a lot
by putting yourself in their shoe... In other word, think more
maturely...
Think about the future instead of current...
Endure ^^
I am sure one day you can get what you want... ^^
Cheers