The echinodorus compacta is the only plant that's aquatic. The others have to have their leaves out of the water.
Also, do you use a filter?
If your fish are gasping, you're doing the right thing to return an airstone.
Perhaps you don't have sufficient filtration... 6 plants in a 70 gallon probably won't provide enough oxygen.
reccomend you find some plants in our plant profiles, and then go look for them. The other plants you purchased will rot submerged. Spathiphullum is actually a peace lily.
For oxygenation, look for plants such as:
Wisteria (Hygrophila Difformis)
Java Fern, Java Moss, crypts, and anubias are also nice, but they tend to be slow growers... They won't be the best oxygenators.
A Liquid fertiliser also helps. Flourish Comprehensive is a good one.