You sold the property in June 2015 for £1,035,000 and made a gain of £861,442 (£1,035,000 sale proceeds - £155,000 purchase price - £18,558 purchase and selling costs). That's £430,721 for each of you. The following figures are for each of you individually:
Total period of ownership to June 2015: 219 months
Period of owner occupation: 36 months
Period of letting: 59 months
Period of vacancy: 124 months (occupied by children and others)
Exempt gain: £106,205 (£430,721 / 219 x 54 (36 + last 18 months of ownership)
Letting period gain: £80,637 (£430,721 / 219 x 41 (59 - last 18 months of ownership)
Vacant period gain: £243,879 (£430,731 / 219 x 124)
Gross Non-Exempt Gain: £324,516 (£80,637 + £243,879)
Letting Relief: £40,000 (lesser of £40,000, £106,205 and £80,637)
Annual CGT Exemption: £11,000
Net Taxable Gain: £273,516
CGT @ 18% or 28% or a combination of the two rates depending on the level of your income in 2015/16. Look here to see how to calculate your CGT rate.
I'll post again in a few minutes to tell you what figures go into what boxes on the CG pages and then you can ask me which of the CG worksheet boxs in the HMRC online return you are having problems with.