Can you see the common theme with this family of court cards?

Yep water and they all look dreamy
Page- not sure how to display his emotions he sways from been emotional to showing no emotion
Knight-Hes willing to cross the line and express his feelings
Queen-Well out of it, surrounded by turbulent water that laps up the shore says she finds it hard to control her emotions
King- He seats him self on a ridged stone that wont move, he puts him self above his emotions ,which are breaking into big waves, so that he doesn't have to Handel them

I agree. They do look all watery and dreamy. Also a lot of peaceful blues in these cards, and yellow, which to me stands for confidence and good self esteem.
page of cups: looks like he's contemplating life, or meditating about something.
knight of cups: White horse for purity and protection. He makes me feel safe.
queen of cups: emotional, moody woman. Wears her heart on her sleeve.
king of cups: He balances his emotions (the cup in his hand) with his sense of fairness and rationality (the staff in his other hand)

Water is the theme.  The page, knight and queen are all looking at their cups where as the king isn't.  the only difference between the king and his court is that he sits on the water and they have water by them.  may mean that he has all that he wants and doesn't worry about it because all he needs is to dip his cup anytime and fill it.  
His page looks at a fish in a cup.  the fish is new and filled with wonder of all the things he may learn and know it his life.  a fish a symbol of spiritualism along with the water as life.  
the knight rides out with his spiritual armor and his cup as his causes or guide into a new world.  
The queen studies more and then some more of her charges: the page, the knight, and her own cup.  a spiritual women with a lot of studying behind and before.

Yes, most definately water based, and perserving what is in their cups.

The Page - He looks a bit awkward holding his cup, so to me suggest someone who has still got a lot to learn, but also knows that it is imprtant to keep his cup in balance while he grows  (A bit stuck on this one)

The Knight - Proud, focused, willing and able to help.  Looks like he would be open to others.  Looks like he is ready to take on new things

The Queen - looks a little distracted, preoccupied with her cup, perhaps doesn't notice too much around her, other than her own interests.  A quiet type, who would keep to herself

The king - Looks like he has everything he needs, he looks confident, and understanding to others, a good listener and wise in his counsel