Well personally I think you cant have 2 Tangs in that space, I would have to disagree with the LFS on that one, maybe I am wrong, its just my opinion. If thats what the LFS said then I am sure they will be more than happy to attach a guarantee with that and give you your money back if it dies!
You have to make the decision; sure you can fit 2 tangs in 50g and they will live, but what is their quality of life going to be like? I know ideally they would like 10000000g but its good to compromise. If they are relatively young it can work for now but may have to look for something bigger in the future.
WOuld be a good idea to speak to our new shark (
) Ophiuora as she is very knowledgable on tangs and may put me right in my place and tlel me im wrong!
All the best,
Tim