What 4 tangs are you looking at getting and sizes? I did 4 yellow tangs in a Biocube 14 (10 gallon actual volume). They were small like 2-2/34” each. At first they were in all swimming together and not fighting. Then a little bickering started and 1 got a bad infection and another was just barely starting to get one. I quickly built a divider and separated each one of them. All 4 completed QT and I had all 4 in my display tank From November 2019 until about April 2020. I now have 3 of them (no, 1 didn’t die) because a local reefer was looking for one and it was when hardly any fish were available due to COVID and flight shortages from overseas. He still has it as well in his 100 gallon Rubbermaid frag tank. So, while I wouldn’t advise someone to do this and it can be considered reckless I guess I still think your 50 gallon Hex would have been just fine with the proper attention paid to details.