Similar here. DP born in UK. His Mum has reasonable English. His Dad lost half his hearing as a teen, and didn't pick up a massive amount of English. They have retired back home to care for the respective parents (DH's Grandparents).
Were here now sob. Tonal language, dialect spoken at home. No books, courses, local speakers other than DH within a 50 mile radius of home, and I'm tone deaf. It's a nightmare to learn. It DS learning the original, not dialect. I'm picking it up with them. But even if I know 1000 words, its not going to help when they keep switching, and wertyu could mean 7 different things depending on tone and context. And politics is a whole different ball game to hello, my name is, what are you called, how are you today?
The language of the house is this dialect. I tune out now, but it drives me up with wall. Today, for example "come on, were going out" where??? "For a walk" OK, is it far "no". Two hours later, with knackered 6 and 4 year olds, I realise they want to do a further loop, and were not even half way? I spat my dummy out. DH also has tears from me on occasion. I don't want to know that the next door neighbours grandmother's nephews brothers pig has had to be taken to the vets. I DO want to know they are planning a full day out tomorrow, and were leaving at 8am!
Were here on " holiday". Whenever people asked where we were going, I got wow, lucky you type responses. The reality is DH and I are sharing a 3/4 double, there is no heating, the shower is dodgy, and the food is great for my waistline. I'm stuck here for 10 days
. We can't stay in a hotel - tried that, even I knew Grandma wasn't impressed when that one came out!!!
Noisy. I'd say you have a couple of choices. It sounds like the learn the language has been tried, and unsupported. So, you could either go out, and do other stuff when they come round. Accept you will feel like the hired help when they visit, or demand the family language is English in your house.
I order to support the kids bilingualism (well, tri, but let's not go into schooling) I use the time when DHs family are at ours to achieve stuff, and leave them to it.
My kindle reading, and MN time has been huge this "holiday". I avoid, because I married my husband because I loved him, and everything his multi language upbringing has made him. I want my kids to have a great start in tonal languages (and let's face it, Mandarin must be one of the most powerful tonal languages in the coming world), and to get all those plusses, there are some minuses. I've taken the passive response, but we are separated by flights and time zones. So this is not a daily occourances. Only you can decide if you want to fight or become passive in your response.
And to those saying " Just learn the language" read what Noisy has said. Not common enough to have resources online line, and an extended family who won't help. Tonal language, so precision really matters, and tutor feed back invaluable. How the fuck is she supposed to learn????