Hi Jes,
Sure, you can incorporate walking, if you like! The rotation I suggested was premised on a simple framework of getting 30-60 minutes of cardio, 5-6 days a week, and weight training the entire body 3 times a week. With that in mind, you can do very many different combinations, using the workouts you own:
Mon/Wed - Challenging cardio, 60mins. Add core work if desired.
Tues/Thurs/Sat - A lighter cardio/weight circuit workout (Body Fusion; Cardio & Weights; Step, Jump & Pump);
OR:
Light cardio, 30 mins (this could be walking, Basic Step, Body Fusion cardio only, segments of Step Blast and/or Step, Jump & Pump)
followed by strength training (the CW weight premixes; SJP weight premixes; Body Fusion weight premixes. Doesn't the BS/BF dvd have additional weight training sessions on it? If so, they would work perfectly here).
Fri - Pilates or yoga or rest; if you have the energy and don't feel like you would be overdoing it, you could put some fun cardio here, ranging from 30-60 mins.
Sun - rest
I also think that if you want to do double sets of the weight workouts you have, that would be fine, as long as you are not new to weight training. What might be better is to combine workouts that focus on the same muscle group, but just a bit differently (eg., CW weights and the BS/BF weight add ons). Always listen to your body and don't try to do too much, too soon.
Enjoy your workouts!
Sandra