Eating vanilla is permissible even though it was mixed with alcohol during preparation for two reasons: 1- alcohol is not najis (impure), 2- alcohol does not have any effect on vanilla.

If alcohol is fully absorbed into the food or drink and has disappeared in it, there is nothing wrong with eating or drinking such things at all. If the essence of the alcohol remains present or its traces may be detected in the mixture, it is haram to consume this food or drink.

It is not permissible to consume foods, drinks and medicines that contain gelatin derived from the skin of pigs or other impure substances. It is possible to manufacture gelatin from animals that are slaughtered in the prescribed manner, and it will serve the same purpose in manufacturing medicine or food. For more, see the detailed answer.