As you can see from John’s links, the A77 II was first supported in Camera Raw 8.5 so you’d need to convert its raw files to DNGs using the DNG Converter 8.5 or newer which you can get here: http://www.adobe.com/downloads/updates
It may be possible to update PSE12 to ACR 8.5 although Adobe’s pages list 8.3. This may be because of the OS requirements for ACR 8.4 and newer which are OSX 10.7+ or Windows 7+.
If I was in your spot, I’d wait for PSE13 as long as your OS is new enough. PSE has been updated Sept 20-something the last few years, which would likely be next week. So make DNGs for a few days and see if Adobe releases the next version of PSE soon. Of course you’ll need to have a new enough OS, not 10.6.8, Windows XP or Vista.