The ultimate/age-old battle of the S"ex"s

(Apologies to anyone who may be offended by the term, baby mama/daddy)

As the wife/husband, do you/should you set boundaries in regard to your partner's baby mama/baby daddy and the In-laws?
If so, what and how do you enforce them without drama?

And what if your husbands/wives/spouses Ex or even any of the In-laws won't respect you or accept your guys relationship, causing unnecessary grief in the hope it will destroy your marriage because they're not happy?

I believe in boundaries, but no need to be possessively nasty. A mutual understanding with the main focus being about the child/children.