mercedeslens is giving you the best advice on this effect. If you make marks on the corner of each card it will make it easier for the Point Tracker to follow. I would also label each card to keep track of them. In general when doing the Motion Tracking you are going to place your video on top of each card so using different colored cards so you can key them out isn't necessary. Assuming the cards are a regular shape using masks should do what you need to hide parts of each video when necessary.
One word of advice when using motion trackers, in general you will want to apply the tracked data to a null object layer instead of the actual video layer you want to follow the cards. This gives you an extra level of control.