Hi there and a warm welcome to the forum
Who is advising you to take out a five year deal? If it is the IP then beware, as IPs are not qualified to give our mortgage or investment advice.
That said, if you can secure a good rate over a five year period, this does buy you some certainty and may not be a bad idea. No-one can predict what is going to happen in the mortgage marketplace over the next five years, so we cannot say whether you will be offered a new mortgage at that time - but I suspect it will be likely if you have a reasonable amount of equity in the property and the salary to support the borrowings.
Not sure what you mean by the pension - the annuity will be included as part of his income for the purposes of working out his disposable income. Could you clarify if he is due to receive a lump sum over the next five years.
The caravan will have to be sold, unless you have good reasons to keep it - and your cars ought to be OK so long as they are not of excessive value. You will, of course, have to maintain the HP payments.
Regards, Melanie Giles, Insolvency Practitioner