Hi and welcome to the forum.
Firstly, if most of the debts are in your name, then only you would be eligible for an IVA as it is for debts over £15,000. You should be able to include the tax payment in it is as well (but not 100% sure on that).
I recommend that you speak to an Insolvency Practitioner. Visit
www.iva.com to see a list of companies.
There are several IP's and Debt Advisors who post on here, Melanie Giles, Size5, Andy Davie and VikiW to name but a few. All come highly recommended. Their details can be found under the experts link on the left hand side of the page.
They will explain all your options to you and advise you as to the best way forward for you.