My wife and I are happily married with two beautiful children (four years and nine months). My wife’s carefree-living sister and then-boyfriend have a son (now six). They rely solely on her parents for support; at six months, the boy’s father left permanently.     
      My sister-in-law, 29, lives at home rent free, works part-time and hardly spends time with her son. Her parents take him to and from a private school (they pay), buy all food, clothing and vacations (Disney World three times).     
      They’ve never taken my kids anywhere or invited them over without us, though we live six houses away!     
      My nephew has behaviour issues and gets sent home from school for being a bully, but my wife and I still regularly invite him to play with our son.      
      My in-laws do nothing for our kids. They’ve said they’re too exhausted from providing for my nephew. We have our own home; both work full-time and constantly juggle schedules to handle daycare, housework, grocery shopping, etc.    
      We’d just like them to spend more quality time with our kids, though it’ll always be unbalanced because my nephew lives with them. We want our kids to know their grandparents.    
      It’s been eating away at my wife. Then, at Christmas, they asked us to look after their dog while they take my nephew on yet another vacation. She confronted them about their double standard. They got angry and defensive, asking, what would we have them do? They said, “It is what it is,” and we just have to accept it.      
      My wife explained that they should encourage her sister to be a better provider for herself and her child. They responded that we’re jealous of my sister-in-law and should be ashamed for picking on a “single mother.” We’ve not been on speaking terms with her parents since.    
      I know it’s depressing my wife. They say we owe her family an apology and an admission that we’ve overreacted, or we’ll continue to ignore one another. How can we break the deadlock in a way both sides can live happily with?
      - At Wits End

Your in-laws are decent people overwhelmed by what they’ve taken on, and misguided in how to handle some of the results.    
      Yes, they’ve been “unfair” to your kids, unintentionally, counting on how you’re both so stable, plus loving and attentive to your children. Meanwhile, they’ve got a slothful daughter taking advantage of them, but are enmeshed with her son.    
      Basically, they’re his “parents” - much older, easily tired and in a situation they don’t know how to change. They can see the boy’s already troubled. No wonder they feel “it is what it is.”     
      Forget comparisons, you’re the lucky ones, here. Apologize because they’re feeling so unappreciated for all their efforts. Bring the two families together at your place - and your kids will know their grandparents.

My parents are always speaking about divorce; my sister and I don’t like to hear it. They’re always screaming and using bad words. My mom and dad like each other, but never agree. I don’t know what to do.
      - Worried Child

You and Sis aren’t responsible for their relationship, though it’s natural that you care about it. Focus instead on your own “jobs:” School, helping with chores and getting along.    
      Parents have private stresses - there could be money problems, work pressures, etc. Some yell and use harsh words just to let off steam. Since they like each other, they’ll try to resolve their differences.

My sister and future maid of honour and my good friend/ future bridesmaid don’t get along. Both are stubborn, strong-willed, opinionated and lack a filter. They make snide remarks about each other.    
      Instead of enjoying the bridal experiences, I'll be too busy dealing with a catfight that’ll ruin things. I've practically begged both of them to be on their best behaviour, and also warned the other bridesmaid, asking her to referee if necessary. I want them all in my party. How do I deal with this?
      - Overwhelmed

Call in a mediator: An aunt, or older family friend, a wedding planner. Someone has to be in authority and shield you from these petty squabbles.  
      When one of these antagonists comes whining to you, put up the hand and tell her to solve it themselves, or get a decision from this neutral party. (It should NOT be the other bridesmaid, or she’ll resent her role).