Their finances are their own to deal with and they are free to apply for credit. However, if you have joint finances anywhere, you might be listed on their credit files as a financial associate and your IVA might be taken into consideration when lenders decide whether to lend or not.
My opinions are merely that .. opinions based on experience. Always seek professional advice.
IVA Completed 23rd July 2013 .... C.C. 10th January 2014