I am informed one imam stays silent regarding divine guidance when 2 are present.
. Raifidi hadith by Imam Sadiq (RH)
حدثنا محمد بن الحسين عن الحسن بن محبوب عن العلاء عن عبد الله بن ابى يعفور عن ابى عبد الله عليه السلام قال كان على بن ابى طالب عليه السلام عالم هذه الامة والعلم يتوارث وليس يمضى منا احد حتى يرى من ولده من يعلم علمه ولا تبقى الارض يوما بغير امام منا تفزع إليه الامة قلت يكون امامان قال لا الا واحدهما صامت لا يتكلم حتى يمضى الاول. (Basa'iru d-Darajat of as-Safar al-Qumi) Abdu l-Lah ibn Abi Ya'fur said that Abu Abdi l-Lah (Jafaru s-Sadiq) said: "Ali ibn Abi Talib was the knowledgeable Imam of this Ummah and the knowledge is inherited. Not one of us passes away until he sees a son who learns his knowledge, and the Earth doesn't last for a day without an Imam from us, with the Ummah seeking refuge towards him." I said: "Can there be two Imams?" He said: "No, unless one of them is silent and refuses to speak until the first one passes away."
But as per Quran there are atleast 2 instances when 2 imams speak about divine guidance at the same time.
When We sent to them two but they denied them, so We strengthened [them] with a third, and they said, "Indeed, we are messengers to you."
Another instance is of that Ibrahim and lut.
But when he (ibrahim) saw that they did not stretch out their hands towards it, he had a mistrust about them and felt a fear of them in his heart. They said, "Don't have any fear: for we have been sent to the people of Lot."
The doubt arises because twelver shia also considers prophets and messengers as imam.
How do twelver shia reconcile between the instances of Quran and their hadith?