The context is to welcome new members at an institution.
Found many ways of saying "welcome": 천만에요, 어서 오세요, 환영합니다, 환영하다.
천만에요: replies to gratitude
어서 오세요: shows hospitality to the guest (welcomes to an arrival or an entering a place.)
환영합니다: also shows hospitality, and is also used to welcome new members to a group.
어서오세요 is mostly used in commercial places like tourist attractions, stores and restaurants, etc.
환영합니다 is more general term for 'welcome'.
Welcome to a new member could be like:
안녕하세요 (greeting), XX와 함께하게 된 것을 환영합니다 (welcomes to be one of XX).