I am great at finding deals in most things but this points/mileage thing reallly has me confused.

We (my DH, myself, 13 year old, 12 year old & 7 year old) has a Timeshare week planed for June in Cancun. I have 114,874 AMEX points. We live in Northen CA. so we could fly out of Oakland, San Francisco, San Jose or Sacramento. When I call the airlines they tell me "well it is 70,000 points now but it could be 25,000 later" What is the best way to utilize my points to get the best deal? When should I shop for my flight. Am I too early? Why is it 70,000 now and 25,000 later? How do I know how many points to transfer?

I would appriciate any education you could give me on this.

Thank you,
Theresa