What are the laws regarding a neighbor's tree limb (a very large limb) that's going across my entire yard and has partcially cracked from the trunk plus another large branch that is encroaching my roof. Who is responsible for the removal .

You are responsible. You are allowed to prune anything over your property line . And if the branch breaks it's considered an act of god. Unless the tree is dead the it's negligence

I think is better if you call the city for that question.

First, consult local county or city tree ordinances depending on where you live. Some localities have regulations for heritage trees or private protected trees based on trunk diameter that require pruning permits. We recommend hiring a certified consulting arborist for an opinion and an ISA Certified Arborist to do the work - find tips on hiring a reliable tree care service at www.sactree.com/hire.