Your tank isnt big enough to house even one of those fish!!
Arowanas need a minimum of a 6 foot tank and even that is considered small, at 10 inches long your arowana should be in nothing less than a 75g tank (48x18x18"). You do realise that silver arowanas can grow to 4 feet long dont you? Arowanas are solitary fish that will fight until one is dead when kept in pairs, some people have has success in keeping arowanas together by housing at least 5 in tanks of around 5 or 6 hundred gallons.
Depending on the species your shovelnose will grow to at least a foot and again should be in nothing less than a 75 gallon tank, the only fish you have that is close to being suitable is the snakehead which should max out at around 8 inches but that really needs a 30 gallon tank (36x12x15").
Whoever sold you these fish should be ashamed of themselves and IMO the store needs closing down. You really need to take all your fish back to the store and exchange them for some smaller fish or buy a much bigger tank.