Finnish word siamilaiset kaksoset comes from Finnish siamilainen, Finnish kaksoset (Twins.)

Detailed word origin of siamilaiset kaksoset

Dictionary entry	Language	Definition
siamilainen	Finnish (fin)	(archaic) Siamese (of or pertaining to Siam) (archaic) Thai (person). Siamese (breed of cat).
kaksoset	Finnish (fin)	Twins.
siamilaiset kaksoset	Finnish (fin)	Conjoined twins, Siamese twins.