Hello, I am Keith, one of the experts on Just Answer, and happy to help you with your question.
Firstly, when you left the UK did you complete a Form P85 and submit same to HMRC? If you did not then you should do so immediately. Fortunately there is no time limit for its submission, it is available on the net and can be filed on line. HMRC will then classify you as non resident.
Unfortunately, you do not own any property in the UK. Your flat in London is owned by an overseas company. On completion of the sale the company will be liable for Capital Gains Tax on the gain made between the selling date and the value as at 6 April 2015.
If the company then decides to buy a property for your children then this is not affected by UK taxation.
My answer takes no account of the taxation regime of the country in which the company is domiciled. This could have a dramatic effect and you should consult a trusted, local practitioner in the matter.
I do hope that I have been able to shed some light on the situation for you.