Are "Taha" and "Yasin" among the names of the Messenger (ﷺ)? What is the evidence for that? And is one sinful for being named after them?

"Taha" and "Yasin" are not among the names of the Messenger of Allah, peace and blessings be upon him, and whatever is mentioned to the contrary is not established. Qadi Iyad transmitted weak narrations in this regard. As for Ibn al-Qayyim, he stated that what common people mention, that Taha and Yasin are among the names of the Prophet, peace and blessings be upon him, is neither sound, nor good, nor mursal (a narration where a Tabi'i narrates directly from the Prophet), nor an athar (report) from a Companion. He stated that they are letters like: "Alif, Lam, Mim" and "Ha, Mim." The preponderant opinion is that naming with them is not prescribed.