Hi freddey
We cannot answer your question as we do not have enough information, you say both your daughters are 'our unofficial carers' , the first question I would ask is do you and your brother receive a SDP with your ESA, if only one of you receive this premium then you would loose it if you moved in together, if you both received it then you would still keep the premium.
I would advise you to seek face to face advice from your local welfare rights unit. If you move into a one bed flat to be together that may cause issues if you need your own space at any time.
Gary
Nothing on this board constitutes legal advice - always consult a professional about specific problems 
