I don't know the Universal package cancellation rules, but you are still 90 days out. Disney packages are fully refundable (except for
trip insurance, I think) up to 45 days out. I looked quickly at the Universal Board, but I didn't see anything about cancellation. I'll try to find that out.
If it were my family, I would keep the reservations at Disney through the 10th, then spend a night at the Universal hotel. This gives you two days of Front of the Line Access if it is an onsite Universal hotel (check-in day and check-out day), which will be plenty of time to see both parks. Universal tickets are about $100 for two days and both parks. If you have a Costco membership and live in the South, the warehouses have three-month tickets for $89. You can take cab over the Universal on the 10th, check-in early to get room keys and go to the parks, then go back on the 11th (unless you are leaving early). Your brother and his family are not inconvenienced since you get over there by yourself - no loss of their vacation time.
That's just what I would do!
Edited to add:
Here is the cancellation info from the hotel portion of the Universal website:
http://www.universalorlando.com/hotels/hotel-resort-information.html?intsrch=cancellation
Cancellation Policy
Days Prior to Stay: Penalties:
6 days or more Full Refund
0- 5 days prior charged one night's room rate plus tax
PLEASE NOTE: Deposits are forfeited if guest checks out of the hotel prior to the check-out date.