They would need to be separated as part of the variation process, and separate dividends offered to each one. This is easy in your wife's case, as her dividend will be based upon the offer being made. In your case, you will need to be left with sufficient income to at least offer the original dividend, or else your IVA will need to be varied as well.
I have successfully separated interlocking IVAs in the past, but we would usually prefer not to if we could help it! As Catullus says it is messy, and you have to be sure that one case is not benefitting unduly to the detriment of the other. Are there any joint creditors as a matter of interest?
Regards, Melanie Giles, Insolvency Practitioner for over 20 years.
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