Will my brother die after taking 5 ecstacy tablets mixed with alcohol?

He could. Ecstasy can cause hyperthermia, kidney and muscle damage, seziure, and heart problems that could result in death, the risk would increase with higher doses. It's playing russian roulette.
Maybe. There is nothing you can do to stop a loved one from doing substance abuse. He will just resent being lectured. This is why things are so hard on family. Go on with your own life and be there for him when or if he stops this insanity.
U would know by now. There is no way to know how much mdma is any one particular tablet, or even if it is really mdma, or whether it has contaminants and/or other drugs in it. How much alcohol? One beer, a case, a gallon of vodka? Ecstacy can be a very dangerous drug, and it doesn't get less dangerous mixed with alcohol. If he won't get help, you could start going to alanon, which can help you, and perhaps him too.