1- In sunni school of thought, they practice whatever their Imam mentions and we cannot change the ruling as per other imam. Is it that we have to follow Rasulullah not the Imam?
2- Is it applied to ahlul bayt as well right? May I know the reason with this situation? Why we cannot follow other Imam thought even though the logic is there? And it is in line with Quran but maybe the hadith narrated do not fit the criteria set by the Imam to accept the hadith.

For sunni school of thought, example Imam Shafei-wudhu is void after a husband touch his wife, Imam Hanafi- wudhu is not void if a husband by touch his wife. I am not sure the TOUCH actually mean what but people around me practice is about the contact of skin to skin.

On the other hand, in the Ahlul bayt school we have Ayatollah. From what I understand we need to follow the most learned Ayotallah in our time. But it come to my understanding that there are a few Ayotallah and who follow Ayotallah Sistani ruling for example cannot change the ruling in certain condition to follow other Ayotallah opinion. Why I am asking because I am living far away from any Ayotallah direct communication. What I have Ayotallah Sistani is the most learned during this time and we have to follow him. To me I am not sure I follow who because I switch to follow the Ahlul Bayt path after reading and listening to lecture from among the famous scholars.

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1- When you follow the Imam, you are following Rasulullah actually.
2- Yes, they are interpreting touch as touching by by any part of body, even shaking hands. Hence, they are considering it spoiling wudhu. The names you mentioned are lecturers. They are not Ayatullah to be followed. You can take the rulings of your reference of taqleed from them, if they are aware of these rulings.
Most of the people are living far away from S. Sistani, or any other Ayats, but they can get their opinions through their representatives, as you are doing now.