Mudskippers require a very specialized setup to thrive, they need at least 10 gallons of WATER per fish and another little portion of land each. They're extremely territorial as well. I recommend at least a 90-100 gallon tank, as long and wide as you can get it. A custom tank might be what you want.
They also require a specific gravity of around 1.015 as well, setup the tank with an aragonite or coral based substrate, even SW sand would work (although harder to aquascape).
Unfourtunatly mudskippers do not do well when kept with other fish, it's difficult to meet both the mudskippers and other fish needs at the same time without a really large tank. Anything that could fit into the mudskippers water would probably be either harassed to death or eaten (if it fits in their mouth).