Are your parents trading through RCI or II? Do they own with a larger company that offers some internal exchange options in the Orlando area? If you don't know which exchange company they use, post the name of their home resort. Someone here may know which exchange company is affiliated with it.
IF they're trading via RCI, the closest (nice) 3BRs are:
Sunterra Cypress Pointe Resort - #2750
Sunterra Cypress Pointe Grandvillas - #3996
Silver Lake Resort - #2610
Embassy Vacation Resort at Grand Beach - #3664
Sunterra Resorts Grand Beach - #6315
Celebration World Resort - #5389 (mixed reviews)
Westgate Vacation Villas - #0899 (very mixed reviews)
A little further away, try:
Oasis Lakes Resort - #4852
Hilton Grand Vacations Club at Sea World - #3517
Orange Lake Country Club - #0670
Summer Bay Resort - #3175
IF they're trading via II, the closest (nice) 3BRs are:
Marriott Imperial Palm Villas - MIP
Sheraton Vistana Resort - VIT
Westgate Town Center - WTG (very mixed reviews)
A little further away, try:
Marriott Grande Vista - MGV
Star Island Resort - STR
Fairfield Star Island Resort - VBR
Wyndham Palms Resort & Country Club - PCC
Ron Jon Resort - TLR (mixed reviews)
Westgate Lakes Resort - RYS (very mixed reviews)
3BR timeshare rooms are never traded from DVC, so onsite is not possible for your 3BR request. IF you could accept a 2BR that sleeps 8 and IF you are not going during the most popular timeframe and IF your parents' timeshare is a prime time week at a 5 Star, very high demand resort, then it's somewhat possible that they may be able to trade into one of the DVC resorts listed above. HTH.