I could not find anything about it using the search, so here is my question:

If you have multiple Lt`s present in a city at the start of the OL turn, is 1 siege token added for every Lt or just one in total?

Each lieutenant may add 1 token, so 3 lieutenants adds 3 tokens.

Thanks for the answer, I was afraid to be it this way.

Just remember that no matter how many Lts are there, you still on make one roll to resolve the seige.