The Hilton Garden Inn is a lovely little property that is walking distance to SeaWorld. They have a shuttle too, but we've always walked. They have a cute little pool and hot tub on site. They have a nice restaurant, American Grill onsite that has tasty reasonably priced food too. I've had dinner there or reasonable room service (nice to eat in after a busy SeaWorld day) if we're not eating in the park. The staff here is great, and rooms are well maintained / super clean. You can even get a room with a view of SeaWorld. With six you would need two rooms. You'd need to check, but I think you either can get a king room or a double double. Parking like the other options you are looking at is free too. Note: Breakfast is not included and is decent but pricey -- buffet somewhere around $20 pp. When we stay here, we bring our own breakfast items or on occasion we have gotten a hotel rate that includes breakfast.
I really like this property. I'm not alone either. Reviews on TripAdvisor are excellent.