Yonah was revived by eliyahu hanavi. He is called “Amitai” to hint to the fact that when Eliyahu revived Yonah, his mother (the Isha Tzarfatis, not Shunamis) said, ‘Now I know you are a man of Hashem who speaks Emes’ Since Eliyahu was considered Yonah’s spiritual father, Yonah is called Yonah Ben Amitai.
Regarding the Isha Shumamis whose son Elisha revived, one opinion says she is the sister of Avishag HaShumamis, though this is farfetched since Avishag lived hundreds of years earlier in the time of Dovid. As others have mentioned, there is a shita that the child’s was Chabakuk the navi. This is hinted by the promise Elisha gave her – ‘next year at this time you will be hugging ‘chobekes’ a son’