The British don’t need to conquer them, as in fact they often don’t. Both states are under threat from Afghans, so the British simply push them to join a subsidiary alliance whereby they surrender a portion of land in their kingdom whose revenue will be used for the upkeep of a British regiment whose sole purpose is to protect these states. In return they cease all contact with foreign courts and allow a British resident to be stationed there. At that point any independence the ruler has is in his ability to go against the will of the residents, backed up by the British regiment thus in his exceptional ability to maintain a standing army that can challenge the British and either establish his own illegal way of getting intelligence or accessing the residents ways fully (it happened otl on occasion but only once or twice not a defining feature of a particular ruler- the nawab of Oudh once knew his resident was being fired before the resident himself). Népal agreed to have a resident after a loss in the Gurkha war but managed to isolate the resident to such an extent he was basically in house arrest. Then again, the situation in nepal was contingent on a buffer state policy with China- what is the fearsome analogue here that makes the Brits unwilling to share a border with them and ensures that they’ll ally with the Brits out of choice- a resurgent Persia or Afghanistan?