Dependant visa for a child

[Micana]

Hello. I ve got some problems if anyone can help me. I'm uzbekistan citizen, married to a british national and i've got ILR. My son lives in Tashkent with my sister. In may i'm flying there to get him. But my problem is that i dont know what kind of OVIR i need for my son and me( 2 years or PMG). If it is for 2 years than my son gets the passport which is valid for few months which wont be accepted by british embassy (they require passport at least for 6 month) What kind of visa he will get from british embassy (i want apply for settlement).
I cant stay there for more than 3 months otherwise it will be a problem to apply for naturalization.

Thanks