The LD50 for benzodiazepines is purposefully very high, to prevent overdosing. Benzodiazepines replaced barbiturates as sleeping medication for a reason; to promote safety; and therefore it isn't that easy to OD on them. I recommend that you consider incorporating them into different methods instead of aiming to OD on them.
I second this. It's good information.
The aggregate success rate of suicide attempts by drug poisoning are 1.5%.
You are very likely to just vomit up the alcohol and benzodiazepines, black out, and wake up feeling like horseshit or in hospital the next day.
Dosage advice is impossible given how unreliable it is at nearly any dose. If you really intend to attempt this method despite the unlikely chance of success, then really the only advice I can say is the more alcohol and the more benzodiazepines you can get down your gullet, the better.
1.5mg of bromazepam is really not even close to the amount you would need to potentiate alcohol to the extent that it could kill you. You would have to be saving your benzos for years before you had a sufficient dose.
