Landing 9am on a Sunday. Any shuls open to daven?
no
Any recommendations for Marriott hotel under 35k points per room with kids?
depending where you need/ want to be....
Interns of space and proximity to food and shuls, Residence Inn Watertown. Ask for an upgrade to a two bedroom suite.
AC Cleveland Circle is walking distance to shuls . You can try and get an upgrade to a suite.
Downtown, there's a couple 35k options but rooms tend to be significantly smaller. Element, Courtyard, Moxy, AC further from shuls and food.