How to set up tns listeners for Multiple Oracle Installations on One machine
You need to have different keys for the IPC entries in the two configurations, e.g. KEY = EXTPROC10 and KEY = EXTPROC11. IPC uses memory and semaphores etc. that may be shared across the machine, so you need to provide a way for the instances to be differentiated.

Also make sure you're starting the listeners explicitly, e.g. lsnrctl start listener10, and you have the environment set properly for your two accounts, including LD_LIBRARY_PATH pointing to the right ORACLE_HOME.