have you not registered him with the British embassy in Manila ? get him a British passport there, so you don't have to pay £500 for a settlement visa for him if you bring your family to the uk

also, if i remember this correctly, your son is British by descent (thru you), so any children he has must be born in the uk to be British, and children he has in the phils or outside the uk will not be British., not unless they can go thru the visa process and be registered as British after many years living in the uk..