Salaam again.
Once i have time i will provide you the reference for the hadith(s) that mention all the 12 Imams by their names. I am not sure of your faith but if you have any contenders for these 12 leaders from the ruling Quraysh, i.e. Bani Abbas, Bani Ummayya then please share the list with us.
2ndly, all the imams before departing chose and left a successor just like all the guides from Allah had done before.