From the compromise perspective I think you need to either not go, but send BF, or you both go with the understanding that there WILL be boundaries.
Pick a reasonable *compromise* time. If his family dinners are normally a 5 hour affair, decide ahead of time what time you will leave, like maybe after 3 hours.
Does everyone know english? In a family situation they should not be leaving you out, and it sounds like you understand *some* of their language? You need to understand EVERY thing that is said, and it sounds like BF needs to play translator. Sure, it's annoying, but it's compromise. If he expects you to go, then he'd darn well better treat you like an equal here. Depending on the details of the language barrier, he can hold up the entirety of his side of the conversation in English and translate everything they say for you (regardless of whether or not it was said to you).
And for you, you should try your best to make conversation with Auntie, even though it sounds like she's got a prejudice against you. Kill them with kindness.
And have a great vacation!