>>Can the standalone servers be configured into a Jboss cluster?
==>Yes, you can use standalone-ha.xml or standalone-full-ha.xml.
>>Can we just copy the standalone-ha.xml into eg server1-ha.xml. server2-ha.xml etc or need to copy the whole standalone directory or need to have Jboss into two separate directories?
==> You can use either way but I recommend that you use latter way because sharing directory might cause other issue. Therefore, separating whole directory is simple and clear solution away from unexpected issues.
Is the farm directory not there to use with standalone server cluster and we have to deploy the app separately into each member?
==>No, there is not farm directory. In order to use singleton application such as quartz, using EJB Timer is a good way and then, deploy the application to each member.
Refer this url : singleton ejb in the cluster