You can control the version of JDK in JBoss EAP by pointing JAVA_HOME to the path of the desired Java version.
You can find JAVA_HOME in the standalone.conf or domain.conf configuration files.
Just bear in mind that instances running different versions of Java should not be clustered together.
In other words, it is not recommended to have a Managed Server of "Host Controller A" and a Manged Server of "Host Controller B" in the same JBoss cluster, running on different version of Java. Such a setup, could lead to issues due to different JDK classes.