First, nannies are mandated reporters. If there are signs of abuse, you are legally required to report it.
http://nanny.org/resources/nannies/reporting-suspected-abuse/
Second, you need to figure ot what you want. If you primarily want to stay, then you need to have a conversation with both MB and DB. You cannot handle this by tattling on him. You need to acknowledge that they are both your employers and behave as if you are a team.
"Thanks for meeting with me! Over the past few months, I've been struggling with some changes in our routine. Now that DB is home between X and Y most days, I find that having the living room be the primary playspace makes it hard not to get in the way of his relaxing with his shows. I was hoping that we could talk about finding a different space in the house to move toys to such and A room or B room, and maybe getting a small table to put in C location so that we can have meals and art projects without the volume level disrupting what you're doing.
What you need here is plausible deniability. You aren't telling MB behind his back, you are INNOCENTLY telling her with him there because of course you ASSUMED that she is familiar with his routine. And of course you aren't judging him for being a waste of space, but are actually just trying so hard not to INCONVENIENCE him.
If you just want to leave, I would have a conversation with MB and explain that you are leaving on X date and that you think a daycare situation where the kids are out of the house might be a better fit for the above reasons.