Question: How do I set realistic expectations for my parents about boundaries for my first child? 

My brother has two kids and they steamroll him - they tell him and his wife how to parent all the time, they purposely buy gifts my brother is against, they ask intrusive questions and say somewhat manipulative things to their kids about being the "favourite" grandparents. 

It pains me to see the stress and self-doubt it causes my brother, and though he won't stand up to them (I've tried to get him to!), I am determined that they are not going to do this with us.

Answer: The main components of boundary-setting are establishment and reinforcement. When establishing boundaries, be matter-of-fact, specific and kind but firm (magical alchemy for even the most difficult of interpersonal situations). 

Make your "rules" feel in step with your general parenting philosophy rather than a knee-jerk reaction to their prior offenses. Effective: "We have a no-X rule for the baby, as I've mentioned. 

Thank you so much for buying this - it's so generous! - but we can't have it in the house. Would you like to return it, or should we?" Not so effective: "Why can't you listen? I told you so many times we don't let Baby play with X. 

This is just like what you do to Joe." The sooner you start, the better - and prepping for the child/grandchild provides plenty of practice in both establishment and reinforcement.