Jools, it sounds as if you would be able to continue on income related ESA, as your husband is not able to work either. The switch-over from (C)ESA to(IR)ESA should be easy and seemless - according to DWP!
The 12 month limitation of (C)ESA for people in WRAG has recently been enacted, it is not something that can be appealed against although, of course, one can still appeal against the decision to be assigned to the WRAG instead of the support group (subject to time constraints) or ask for a supercession if one's condition has deteriorated since the original decision was made.
ESA and DLA are totally seperate, there is no reason (from what you have said) to suppose that your husband will lose his DLA, even if you do not qualify for (IR)ESA for any reason.
Nothing on this board constitutes legal advice - always consult a professional about specific problems 
