Hi.PROPERTY LET FOR 4 YEARSA property that is let cannot by definition be your main residence. A married couple can also only have one main residence between them at any one time. A nomination needs to be made within two years of acquiring a new home.Assuming the property that you moved out of four years ago was your main home from the date you bought it until you moved out, then the gain for the period that you lived in it will be exempt from CGT. In addition, the gain for the last 36 months of ownership will also be exempt from CGT if you sell it by 5 April 2014. From 6 April 2014, the exemption for the last 36 months of ownership relief will be reduced to an 18 month exemption.As the property has been both your main residence and let you are entitled to a deduction from any otherwise taxable gain called letting relief which is the lesser of:1 £40,000,2 the sum of the main residence gain and the gain for the last 36 (18) months of ownership of the property and3 the gain for the period you let the property less any part covered by the last 36 (18) months of ownership.Take a look at the HMRC helpsheet HS283 for more information on the main residence and CGT.PROPERTY BOUGHT 6 YEARS AGOIf you gift your sons a share of the property, you will be treated as having made a disposal of a percentage of the property for Capital Gains Tax purposes at the open market value with potential CGT consequences for you depending on the increase in value of the property since you bought it, as well as gift for Inheritance Tax purposes. If you did not live for seven years afater making such a gift, the value of the gift would remain in your estate for IHT purposes. Having your sons take responsibility for some of the mortgage will need to be agreed with your lender. However, as a transfer of a mortgage is treated as a cash transaction, there may be stamp duty implications depending on the value transferred. Take a look here for more information on the stamp duty implications when property is transferred for money or money's worth (a mortgage for example).I hope this helps but let me know if you have any further questions.