One person can not hold the position of preisdent at a time in two different NGOs. It is because of the reason of conflict of interest.
Though a person could be a member in different NGOs at same time but the position of president is managerial in nature and therefore, a person is not expected to give proper time to each NGO. Unlike a member of a NGO, where there is no need to take active part in managerial activities. It is setting up long term goals while management is to acheive these.
It is therefore, restricted by laws to be a member of management in two different NGOs at same time.
Being a president of two different NGO’s at the same time is a complex task. They are the officers of the organizations as they serve and do their duties towards the organisation. Officers legally owe a duty of utmost loyalty to their organizations. When a person owes this duty to multiple organizations, complying with it can be a very complex task.
An exception is that unless a contract with, or the internal rules and regulations of, either of the NGOs prohibit you from doing so, you can serve as secretary of both NGOs.