I am sorry that I cannot recommend an IVA company, as I am an insolvency practitioner and not allowed to advertise on the site - but you can find a list of reviews on all practising insolvency practitioners on
www.iva.com.
Whether you are suitable for an IVA, or indeed whether one is appropriate for you, is probably better discussed with an insolvency practitioner who will be able to take time to understand your current financial difficulties and appraise accordingly - delievering the full range of financial solutions available to you.
Your mother-in-law will be a creditor in her own right, but will have to rank side by side with your other creditors for dividend purposes, and could even be asked to step aside and wait until the end of the IVA to start to be repaid. If this would cause her financial hardship, presuming that she would struggle to maintain her loan repayments without your regular contributions which would not be allowed under an IVA, then this is a point for serious consideration given the size of her debt. It is always dangerous to take out loans for other people I am afraid.
An IVA would usually run over a 5 year period, and if you were to earn overtime a proportion of this would also need to be paid into the IVA, and I cannot see you having a problem in arranging another mortgage with your current leder when the existing one expires. The IVA may not affect this greatly, but best to check that out with your lender themselves.
Good luck in your search, and I hope you find the right professional to represent you.