Usually your income should be of no further interest to the IP, having used it initially to calculate your fair share of expenses. At least one firm, however, works on household income, unfairly in my opinion in which case they will still want to know.
My opinions are merely that .. opinions based on experience. Always seek professional advice.
IVA Completed 23rd July 2013 .... C.C. 10th January 2014 http://foggy.blogs.iva.co.uk
Your Husbands IVA company have no legal right or any way to force you to divulge your income. You can refuse to co-operate with their requests and just be calculated at 50% of the bills as a factor for them to work out his disposable income.
Last Payment made 04/12/14. Completion Certificate 25/7/15. IVA company GT. No Issues