I would guess as long as you have cover(plants and decorations) the neons will "outrun" any shark attacks. If you dont have alot of plants plastic or real I would reccomend them. Neons like heavy planted tanks. The bigger fish rule always applies, If a fish is small enogh to fit in another fishes mouth, it just may end up there.

It always helps to know the tank size and decor specs, but in general it should work. Rainbow sharks are said to be more agressive than red tail and both can be fighters, but neither will get big enough to actualy attack the neons with intent to consume. I would recomend the red tail, and only one of them as they are overly agressive towards their own kind as they age. If your tank is under 30G theres no way any shark will work, but as long as there is enough rockwork/planting and enough space for the other fish to stay out of what will be a very strict territory everything will be fine.

My tank is a 55 gallon tank and my fish i have in it are 4 platies, 4 swordtails, 12 neons, 4 gouramis, 3 black phantom tetras, pleco, clown loach and cory cats.