My boys are pad and outdoor trained, but not trained to go on command. It is possible to re-train to 100% outdoors using much of the same method you are now. You can take them outside together if you think they will stay near you and listen to your potty command. If not, you could try using an xpen to keep them together in a smallish area while training.
As suggested above, you can take the pad outdoors to indicate the spot. There are also other aids like special scented bricks to designate a spot.
Potty Rock
If you are going to use a pad at all, I would always always make it available. It is too confusing for the pad to be available sometimes, but not others.
If you prefer to do 100% outdoors, start moving the pad toward the door a little each day. Then eventually take it away completely.