If I am not mistaken, you have raised the tax enquiry query in this forum not so long ago.
Please do not be under any illusion that the Inspector will make you produce the joint bank statements either voluntarily or forcibly or most likely by threats of commissioners hearings and making excessive determinations. Personally, I do not see any point in resisting his demands, sorry, I should say requests.
You say that the Inspector has sent in an apologetic letter! Don't be fooled by this. The Inspector knows exactly what he is doing.
It seems very clear to me that you have a difficult time ahead on the basis of what very little mentioned here, let alone the details not mentioned by you.
The Inspector will look at unexplained lodgements with suspicion. You will also appreciate that the Inspector is used to hearing the same story almost in every enquiry of this nature, ie money has been given by family or it has been won on horses and gambling or it is loans from friends. This is not to say that you are lying, but the Inspector will not simply take your word for it.
Hoping for the best will not take you anywhere. If you do not already have an Accountant, you are best advised to retain one. However, like in any disputed matters, you will need to balance the tax demands against the strain of the enquiry and the costs of professional representation.
My best advice is to own up to receiving the rents if indeed this has been the case. It is never too late for this. If there is definitely nothing to hide, make an effort to explain the accumulation in the savings accounts of the family, including children if you have any.
I would also look at the accumulation of savings year by year over few years prior to the enquiry because the Inspector will most probably move towards this in due course.