Hi there, Tracey!
You sure can buy 2 separate sets of 5-day Theme Park tickets. Tickets have to be used within 14-days of their first use, but if you put the tickets away and don't use them, they'll still be valid next year.
One thing you may want to consider is purchasing Annual Passes instead. I've calculated the pricing for our family and when we were planning on visiting Walt Disney World more than 10 days in a 365-day time frame, it was a better value for us. If your two vacations are within a 365-day period, it might be worth it for you too! There are lots of added benefits to take into consideration as an Annual Passholder too! You can check out the
Annual Passholder benefits on the Walt Disney World website to see if it's worth the cost for your family.
Thanks for stopping by the Moms Panel and I sure hope this helps, Tracey! Please let us know if you need help with any other planning!
Wishing you and your family two Pixie Dusted vacations!
~Jackie