Generally, it's a good idea to reach out to the other PM and let them know if you're planning to make significant changes to a profile they manage. However, if what you're adding contributes to and does not take away from anything existing on that profile, it becomes a bit of a courtesy thing and more of a judgment call than anything else.
For example, if this marriage information you would like to add is perfectly in line with either source documentation you are going to provide or source documentation already on the profile, or even lines up perfectly with the birth dates and birth places of children on the profile, then the information you're about to provide would not conflict with data already provided and I'd feel pretty comfortable adding it. I'd definitely take advantage of the explanation box when adding to someone else's profile, just so that there's good communication on what's being done and why.
But if your marriage info indicates that the couple were married only after the birth of their second child, or conflicts with existing source material on the project, or even would replace existing information on the project, then I would DEFINITELY contact the PM and discuss it with them prior to making any significant changes like that.
I generally appreciate it when someone adds to profiles I manage, especially when it's to make them more accurate and add sources that I wasn't able to find. I hope most will feel the same way, too.