the lion, i don't know, maybe, but the only problem with him, in this tank is that he will eant anything he can fit in his mouth, so you need larger fish with him, a 75 only has enough room for maybe 2 larger fish, one being your tang
as for the trigger and another tang, i'd say i wouldn't, tangs don't mix well, and they need alot of room, i'd look for a vouple of smaller species of fishm aybe a dwarf angel and a couple of smaller species, but taht is just my opinion, i too have a75 gallon, and it is mostly smaller fish(not too many) ane we are getting a koles(i think) tang for it maybe this weekend(or next)