How To Tell My Brother

What is there to tell your brother here?

He is an adult, and he has chosen to be selfish, yet ignores his own FOO. However, he takes his FOO and their pampering for granted. Looks like, he will run away from his FOO, rather escape from his responsibilities when the reality hits him hard.
It is his choice.
Blame your parents for raising an irresponsible son like him. Blame them for being blind-eyed, despite of all the signs he showed about his future relationship with them.

Here, you have so much to tell your parents.
First of all, ask them stop funding your bro immediately.
Even if it is taken in the form of loan, they should be vigilant now.
They should prepare for their old age from now on, and save a good retirement fund.
Most importantly, they should not depend on their son during their old age.

Secondly they should start to value their children for who they are, and not for what gender they belong to.

And finally, they should tell their would-be son-in-low, that their own son is selfish. Thus his behavior shouldn't determine his decision to marry their DD at all.
Instead of blaming the DIL of the house, it is important to understand the son.

A son, who expects his old father to fund his wedding is utterly irresponsible and selfish. Period
The entry of his wife hasn't changed him.
If at all someone is to be blamed for this mess, it should be your bro. No one else.