I always call Jetblue when my fares go down...and I get the difference applied to my account.
As far as which is better to book..together or individually.
I would book everyone under the same reservation. If there are any changes, you may not all be moved together.
I booked my flight to Orlando last spring. Last month, I decided that my dd was going to be able to go with me, so booked her flight. Now, every time there is any type of change, we get two different email notifications. And if there were to be a flight cancellation, or an equipment change, we would be very likely to end up in different areas of the plane, or possibly on two different flights!!!
I called JB to see if I could have the two reservations linked to each other. Nope, not possible. I would have had to cancel them both, rebook and pay any differences in cost. So, save yourself some trouble down the line and book 'em all together.