Hi, 'former' and 'old' don't mean the same thing in english and are not usually interchangeable. In this context, 'former' means 'was before and isn't now' basically, and 'old' means 'have been for a while and still are'. Is this sentence saying that 'the people who were members before (but not now) are not here'?
Yaşlı is the opposite of young, and eski is the opposite of new. People can be eski, objects can be yaşlı; anything can be either of them. When I say "eski karım", it means my ex-wife, not the current one. But if I say "yaşlı karım", it would mean "my wife who is at an old age."
I think "burda" is how "burada" often gets said in everyday speech, but that it technically isn't considered "correct," sort of like how I as an English speaker could say "I'm'nna do it after breakfast" perfectly happily but it wouldn't occur to me to write it down that way (I'd probably write "I'm going to do it after breakfast," or possibly "I'm gonna do it after breakfast," depending on how informal I wanted to be).