Who Should Pay for the Wedding?

Assalamu alaikum, everyone. My elder brother keeps pressuring our mother, claiming that parents are responsible for covering all wedding expenses for their son. He insists he shouldn't pay anything because it's the parents' duty. My mother honestly doesn't have that kind of money. We're four siblings, and he's the oldest. He has a good income, enough to support himself and his future wife, and he's been working for three years. Yet he says our parents should handle the extra household costs after he marries-basically, he doesn't contribute financially now and doesn't plan to later. He says it's their obligation. He's mentally tormenting our mom. Our dad is paralyzed and not fully aware, so my brother ignores him in decisions. I want to know: is there any truth to this 'obligation'? Are parents truly required to pay for their son's wedding even when he has savings (which he's saving for a honeymoon, not the wedding) and earns well? JazakAllah khair for any advice.