The is an art to combining Tangs in an aquarium, so lets discuss specifics. To answer your question, YES, you can have a Hippo Tang, Desjardini Sailfin, Powder Blue (or Brown), and Kole all in your aquarium. I'm not sure if you have achieved this mix of fish on purpose or by conicidence, but each of these Tangs is from a different Genus, which makes them much more apt to get along in captivity.
Your existing Hippo Tang is in a Genus of its own, the Paracanthurus genus. It is very closely related to the Power Blue and Brown Tangs, which are Acanthurus tangs. For this reason, I would be most cautious when adding this mix together on your list. You may want to add 2 or 3 Tangs at the same time, introducing the Powder Blue in this mix. I strongly suggest a Powder Blue, because the Powder Brown is EXTREMELY difficult to keep. For the record, the
Clown Tang is also an Acanthurus Tang, so it should added at the same time as the Powder Blue for best chance at success. Also, you should know that the Acanthurus genus as a whole is more difficult to keep than the other members of the family. They take much longer to acclimate to captivity and are prone to internal parasites.
The Desjardini
Sailfin Tang is a Zebrasoma, the most territorial on your list. I would suggest adding this fish last, or adding a smaller size. For example, I added a
Yellow Tang to my 180 first, but it was much smaller in size than the future Tang additions. If you want to keep a
Purple Tang or
Yellow Tang in your tank, you should add these fish at the same time as the Desjardini. By the way, the Desjardini is extremely durable and will be a great fish for you.
The Kohl Tang is from the Ctenochaetus genus, which are the smallest of the Tangs and the best algae eaters for a reef setting. They are also rather passive in comparison, so you may want to add the Kohl Tang first. You may also find the Chevron and Tomini Tangs available at the LFS, each of which are Ctenochaetus.
The only genus you did not mention that is commonly available is the Naso genus of Tang, which includes the "Naso" Tang and the
Unicorn Tang species. This genus grows rather large and is probably best left out of a 150 gallon tank. I had to think long and hard about adding a
Naso Tang to my 180, and I feel that a 180 is the absolute smallest size aquarium that this genus of fish would be comfortable in.
Just remember, when mixing Tangs of the same genus, add them to the aquarium at the same time. Also, do not add Tangs that are similar in color, such as the
Yellow Tang and Lemon Tang, despite being from a different genus.
This link may help with the scientific names:
Surgeonfish, Tangs, Unicornfish and Moorish Idols 
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