“does that apply to Siamese twins too, if one feels pain the other one does too”
short answer it depends
Longer answer pain is perceived/recieved by nocioreceptors in the skin and travels to spinal cord via nerves then to the brain where it is “felt” ie sensed
So if there is one brain then certainly any pain received by either bod will be felt by the one brain.
If there are two brains it depends on where the nerves travel. Generally bellow the level of where they are conjoined pain will be sensed by both. though even there rt sided pain may be percieved by one brain and left by the other.
Pain above the level of where they are conjoined like hot water on one head of a two headed set. would generally not be sensed by the other head
for example wit hone of the most famous such sets Abby and Brittany Hensel each has touch on one side (I beleive it is the ipsilateral ie same) side