Thank you again,
First, if he is tender with his back legs and playing less, I'd be wary of whether he has had a trauma that he's not telling us about. Especially since this could cause all the signs we are seeing. Since if he has also hit his head and sustained a swelling or small bleed in the brain, it could cause the head tilt as well as bruising/soreness elsewhere.
That said, if this has been going on for weeks and there has been no improvement (especially with his back legs), then we have to be concerned about other issues. This is because head tilts can be caused by ear troubles (less likely here), middle ear infections
, but also issues in the brain.
Further to traumatic injury, we can see brain based bacterial or viral infections (ie FIP, FIV, FeLV). As well, we do see protozoa (ie Toxoplasma) and even parasitic cysts in the brain cause tilts of the head. And I would note that if any of these were present (and depending where in the brain), they could cause lethargy and affect his use of his back legs (not the muscles per say, but affect the nerve impulses that reach those legs.
So, these would be our concerns with what you are seeing with Edward. Therefore, if this has been lingering for weeks without improvement, I do think a check with his vet would be ideal. If they can rule out those above worries, then he may benefit from a cat safe anti-inflammatory to generally reduce inflammation at all these sites +/- antibiotics or anti-protozoal treatments to address which is present and get him feeling back to normal.
Please take care,