GK Unless you have invoices/receipts for equipment and services i do not think there is away of getting your wife's contribution to care costs reduced.
One possibility may be have her requirements reviewed to include nighttime needs and get an increase in direct payments for that. I am not however convinced of the ethics of doing that and retaining the extra direct payment for yourselves. because as you are married and I presume still a couple you would probably have agreed to care for each other in your Wedding Vows
Am going through something fairly similar and from my enquiries from social services it is permissible for someone recieving direct payments to officially employ a family member to provide care however that family member cannot live at the same address and they require official proof of other address. That may be peculiar to my LA, but you could always ask
