For example, say I work with a group of people, and one completes a very successful project. If I feel happy that a teammate has had a success I then I am…..?
It is possible that you are vicariously happy. Something that is vicarious is, according to Merriam-Webster,
experienced or felt by watching, hearing about, or reading about someone else rather than by doing something yourself.
So, to be vicariously happy is to be happy for someone else's achievement as though it were your own.
I'm surprised to not see naches on this list. It's a loan-word from Yiddish, usually used for mentees or ones children, to express the happiness felt when they succeed.
Feeling of contentment at another's successes.