Opening Employee Balances (Leaves & Advances)

How to migrate opening employee advances into erpnext. As opening balances against employees.

Also for earned leaves, the carry forwarded leaves from last 5 years need to be added as opening balance.

What are the easiest way of doing these ?

The easiest way for leaves would be to import an Excel file for the leave allocation doctype, which should allocate the proper leave balances for each employees.

For employee advances, you can directly create JVs for the sanctioned employee advances against the temporary opening account, which can be balanced against your opening balance entry.
If you want to keep track of the unsanctioned amount, requested amount as well, then importing an Excel file for the employee advances doctype would be the way to go.