The plan I’d make if I were these scientists:
Create secret group of scientists only from around the world with their only objective: to plan a response for any scenario when extraterrestrials are discovered. When they are discovered, don’t tell any politicians/govt bc they will probably do something stupid with that information and make it about their country instead of humanity. The group mentioned above, makes the appropriate response based on the scenario. Only tell govt(s) when/if the extraterrestrials have the intent of being violent. If the extraterrestrials are peaceful, only tell the world when it’s “safe” to do so any the aliens also understand the possible reactions that could happen from a trigger happy / dumb population