DH and I are in our late 20s, he is an only child after having an older brother who passed away a decade ago. I say this for context because it may be that they've become very attached to DH, and by extension, me. His parents are well-meaning people BUT they are extremely instructive about the smallest details to the point where I find it difficult to be in their company for extended periods of time. I have really never seen anything like it. Some examples include if we're eating dinner they will tell us when to go wash our hands, if we're out at a family barbeque my MIL will tell DH to stay out of the sun and when to put on a jacket, FIL has sent me messages to tell me to take an umbrella if he sees it's raining, if we're around other people my MIL will 'prompt' me to greet them as if I don't know that I should be saying hello to them and she will even adjust my plate while I'm eating if she doesn't think it's sitting at the right angle. They also don't have a filter at all or much of a sense of personal space e.g my MIL will point out if I have a pimple, she's fiddled with my necklace if it's skewed etc.
I've asked DH how he's lived with it and he says he just tunes a lot of it out and picks his battles, but I find it so stressful and irritating. They are from a culture where the style of parenting is fairly authoritarian but even so, it's very difficult to deal with. I try and just brush each thing off as it comes but before I know it, the next instruction is being issued 
How on earth do you deal with people like this without losing your sanity? They genuinely don't seem to think there is anything odd about their behaviour and think that they are being caring. We have lived abroad and in different cities but it's always the same when we come back.