You can use the following command to list the accounts:
$ curl -X POST --data '{"jsonrpc":"2.0","method":"eth_accounts","params":[],"id":1} http://127.0.0.1:8545'
Output:
{
"id":1,
"jsonrpc": "2.0",
"result": ["0x407d73d8a49eeb85d32cf465507dd71d507100c1"]
}
I don't see why you don't want to use geth even when there are different geth process running. It shouldn't make any difference.