@jnicholes - Jared. You are getting these for your Mother? Do as much research as you can and summarize for her. One thing not mentioned directly so far is watering. These plants require vastly different amounts - the Snake plant very little compared to the peace lily. For most people growing house plants, the biggest killer is watering - and the worst of the two is over watering versus under watering.
Fortunately, these are all fairly easy for anyone to grow. From my personal experience with all of them, the Snake and Pothos are the easiest.
Without specific variety info, some of your questions are hard to answer. The ATP plant database will likely help. The peace lily will likely be the first needing repotting as they expand with offsets fairly quickly.
The air will certainly be more refreshing as they produce more oxygen while removing carbon dioxide and some other gases from the air.
Depending on the varieties, the Snake or Parlor Palm will get the biggest. If the Peace lily is a large variety, it can also get quite large. Chances are it is a smaller variety.
Good luck
