As a new hire, what is your best course?
First take it slow and keep a level head. Don't get anxious because others are.
Put ideas out there--keep moving forward.
Stay neutral in long-standing smackdowns--these were before your time, stay clear.
Try to help out--you may be regarded with resentment--sure, you get a nice job now, but you should have been here before, are you here to fire me, replace me, show me up?
If everyone has an attitude, make a point to find one lifeline person you can talk to about things.
And try to stay positive--the existing employees are all set in their roles--don't come on too strong, just do your job.
Gradually things should turn.