Thanks for you waiiting, I'm afriad I've had an unexpetadly busy day.
Your son is not in a good position I am sorry to say.
In order tor a person to claim indefinate leave to remain on the basis of long residence in the UK they must have been here for 10 continuous years, which your son obviosuly does not have.
Time spent in the UK on a PSW visa cannot be counted towards and application for ILR, other than under the long residence rule above.
If he does not meet the required points in order to extend his visa or otherwise apply as a sponsored skilled work sponsored by his employer then his best shot is to submit a Discretionary Application for further leave to remain. This would be an application outside of the traditional methods of obtaining leave to remain (ie. those available on the UKBA website).
His argument would be that he should be permitted leave to remain in the UK on the basis of his Human Right to a family and private life so that he can remain as part of your family. He would have to show that he does not have any family or friends in Russia to the extent that his life their has effectively ceased and, further, show that he cannot accomodate and support himself (with assitance from you) so that he need not access public funds.
This is a difficult applicatoin to make and you woulc certainly need a solicitor to do it on your behalf because it's a specialist application. It would cost in the region of £1000-1500 + Vat for a solicitor to act on his behalf. It is by no means certain of sucess but if he does not meet the eligibility crtieria otherwise then it may be his only chance.
Obviously, you do not have to worry about clicking accept to this.