As far as I know, it cannot be possible. Once you use the same interface information for 2 different Portals and Gateways, you will receive these errors while committing the configuration:
Error: GlobalProtect portal 'Portal1' has used dynamic interface ethernet1/1 as GlobalProtect portal 'Portal2'
Error: GlobalProtect gateway 'tunnel.10' has used dynamic interface ethernet1/1 as GlobalProtect gateway 'tunnel.20'
If you use non-dynamic interfaces, you will not even see the IP address in the second Portal or Gateway's IP address drow down menu.
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