Hi Johnkim4,
Since you proactively sought out these alumni, there's a good chance they may never even communicate the meeting back to the school, so I wouldn't worry too much about avoiding certain topics, as long as you use regular discretion. 
These meetings would be a great opportunity to learn about their experiences, what they liked about the program, how they've leveraged the alumni network, etc. Take good notes -- as this could provide great material for your essays. 
Daniel Richards
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