Living in a 5-bedroom rental with my BF, his enmeshed mother, and his 31yo man-child brother. The boundary layout is a nightmare.

[Anonymous]

She acts as a full-service concierge for a 31-year-old grown man (my partner's brother). By doing his laundry, ironing his clothes, cooking every single meal, cleaning his room, and even prepping days' worth of food like an automatic pet feeder when she’s away, she ensures he never has to develop a single adult survival skill. She has trained him into total learned helplessness.
She has completely shattered normal family boundaries by shifting their daily routine from the living room into the isolation of the bedroom. Eating breakfast and dinner together every single day inside a bedroom, a space she must physically walk through to access the rest of the house, she has essentially cast her son into a "surrogate partner" role to fulfill her own emotional needs, shutting out the rest of the household.

I've tried to get my partner to stop it, but he's saying it's no big deal and I should look at it as her doing housework.

[Sanch62]

Why subject yourself to living there with her?

[ExpatInItaly]

It's not your business. 

[stillafool]

Dang, I wish his mom lived with me.  Does she also make your meals and do your laundry?

[basil67]

How is this issue affecting you?

 

[introverted1]

The easy fix it is for you to move out, with or without your bf.  Why do you stay? 

[ShyViolet]

If this bothers you so much then don't live there.

The relationship your boyfriend's brother has with his mother is honestly not your business, as long as it doesn't directly affect you.  I think you'll find that your life is easier if you decide not to care about it.