2 GBR in a 90g!? They will look so small.
I personally love the look and behaviour of Yoyos. I have a dozen in my 90g. $3/1.99 for healthy little guys, why not.
The more you have, the more they play together and leave other fish alone. If you only have a few in a 90g, they will be 'bored' frequently if they can't see others of their own. This applies to a few types of loaches, I think polkadots too.
I know what you mean about the names, There's the scientific term, then all the common names. Some keep the actual name, others use the more customer friendly names like Rainbow shark or Yellow lab.