They really will need to get used to being brushed. If they get matted, they need to be shaved down, and that is not something that is easy anyway, let alone with a rabbit that is not used to any grooming. It's just something that has to be done with longer furred rabbits. If you can't keep them brushed out, you need to keep them clipped short and that would need to be done every couple months.
Pineapple really does not prevent or treat problems. The enzymes need to be quite hot to work, and that sort of temperature does not occur in a living rabbit. Hay, water, and regular grooming are the best options to prevent problems.