Vietnamese Coins, How Do I Authenticate These?

Thanks! :)

The one you can't read the nametag for - the one on the left - is Minh Mang (1820-1841).

I was trying to get some sense of scale of these pieces - next time, please consider placing a ruler down next to your unidentified coins while you're talking. The large silvery things above them are Ike dollars, right? That would make these things much bigger than Ikes. Vietnamese cash coins are typically the same size or smaller than Chinese and Japanese cash. Some larger multiple-cash coins were made for some rulers, but genuine ones are typically very scarce. Very few coins of any kind were made for emperor Ham Nghi (palace records show only 24,000 small cash were made, during his brief escape from French custody).

Your coins are, sadly, all replicas. Large coin-like replicas such as these are typically made for attaching to houses for good luck.