Ouch, sorry about your wrists and knees.
Arnica gel is good for bruises and sore parts.
Tape your wrists or use a wrist brace, mobility will be decreased, ergo less chance of punishment. And of course, rest (don't use them for a while, train something else). "Train in a way that makes you stronger, not destroy your body." I read that somewhere.
Wrist flexibility is good. But whole body relaxation and flexibility is even better, so when they crank on your wrist you receive the force with the whole body, not just the wrist! Even better, develop aiki and body conditioning that allows you to redirect their energy so their nikyo or sankyo "goes somewhere else" (I wish I could do this).
Are your knees hurting because of over-use, misuse, or from hitting a surface? I only use knee pads when doing seated stuff on wooden floor. On the mat I have no problem, but they should not hit hard anyway... don't drive your knees onto the mat for falling or throwing. When moving, knees move back and forth in line with feet, they do not twist in/out (they are not designed to do that).