The gain made on the sale of a property is treated as having accrued evenly over the entire period of ownership but you won't pay CGT on all the gain from the sale of the 1986 property, if any. Divide the gain in two, half for each of yourself and your wife, assuming the property has been in joint names since you bought it. Divide each half into months of ownership to arrive at the monthly gain for each of you. The following will apply to your respective shares of the gain:
The gain for the period that you lived in the property will be exempt from CGT as will the gain for the last 18 months of ownership of the property. So, if you sell it by around October/November 2015 (18 months from when you moved out to be exact), there will be no CGT to pay.
As the property will have been both your main home and let, you will each be entitled to a further deduction from the gain called letting relief and this will be the lesser of:
2 the sum of the gain for the period that you lived in the property and the gain for the last 18 months of ownership and
3 that part of the letting period gain not covered by the last 18 months of ownership.
Letting relief will only be needed if you don't sell the property within 18 months of moving out of it. The first £11,100 of each of your remaining gains will be exempt from CGT assuming a sale in the 2015/16 tax year.
Take a look at HS283
for more information on the main home and CGT. Note that it mentions an exemption for the last 36 months of ownership. This was reduced to 18 months for disposals after 5 April 2014 due to abuse by property owners with several properties. The 2014/15 version of HS283 has yet to be published.
I hope this helps but let me know if you have any further questions.