Hi Julie
Whilst there are allergic and parasite causes of baldness and skin irritation, there are also stress related causes of overgrooming that could be significant for your cat's problem since your move in January and/or in relation to the interaction between your 2 cats. Get your vets to take another look at the problem but also ask what they think about this possibility. Some feline pheromone therapy may help here.
Cathy Wickenden BVet Med MRCVS
Barton Lodge Veterinary Centre
1 Midland Road, Hemel Hempstead, Hertfordshire, HP2 5BH
Tel: 01442 216048 24 hours
[
www.bartonlodgevets.co.uk]