What are the dimensions? If it is only 4' long, then the only Tang I would do is a smaller Bristletooth. Powder Brown (and other 8-12" Tangs) should be in a 6' long tank minimum IMO.
I have 4 tangs in a 180 so I would say yes, two would be possible. Just not those two. A naso is really only suited for 180 gallon or larger tanks and I would even call 180 the BARE minimum for a small adult. Consider a Zebrasoma variety possibly.
I have a 12 inch Naso in my 8 foot long 400 gallon. After watching it for a month, it's too small. These fish need to be in a longer aquarium or left in the wild. I love the Tang, it's not getting the swimming room it wants. Just my 2 cents
Agree with above comments, though you may be fine short term with 3-4 Tangs of different species longer term I'd only suggest maybe a Yellow along with a Kole or Tomini. Even these smaller Tangs are not best kept in smaller than 120-150g DT's as they will get bored and aggressive with such small territories. I have five Tangs in my 125g, two of which need to be upgraded to larger tanks already and eventually all will be in a much larger system.