Dangerous trees in yard - withhold rent

Greetings, I'm writing to request some guidance on whether I am about to overstep my bounds as a tenant. I am renting a single-family home in Middlesex County with my family. Our landlords previsouly resided in the home, but moved out of state and began renting several years ago - managing the property through thier relationships with local service providers. The house is older and has had multiple issues, but the landlords have been fairly responsive with our concerns in the past. About one month ago, we requested that the lanlords have an arborist come out to the house because several trees in the back yard showed evidence of rotting/dead limbs or worse. Over a week later, a very large tree limb (that I had previously not been worried about) came crashing down overnight and crushed a portion of a children's swingset in the backyard. Once again contact with the landlords was made, at which time they asked us to drag the tree limb to the back of the yard so they could cut it up this spring when they are in town. I clarified that there were several limbs remaining that required removal, and that the entire tree may have to come down, but that an arborist was needed to evaluate the trees in the yard at any rate. About another week passed with no contact from the landlords. I then called the landlords and left a message on a Friday night regarding the need for an arborist, and had received no response as of the following Tuesday, thre weeks to a month after we first expressed concerns over the trees in the yard. I called the landlords again and have yet to receive a response. My plan now is to e-mail the landlords and let them know that I plan to hire an arborist to evaluate the trees, remove the limbs/trees that are deemed unsound, and deduct the cost from our monthly rent payment. I hate to do this, but I have small children, and I cannot let them play in the yard until this issue has been resolved. I know I'm on dangerous ground here, though, because I am proposing to irreversibly alter the landscape of the property, possibly against the wishes of the landlords (I don't know for sure, because apparently they won't return my calls). I feel that these trees pose an obvious safety hazard (especially in light of the limb partially crushing the swingset) and am within my rights to take steps to rectify the situation in the absence of a timely response on the part of my landlords, but I'm not sure what technically constitutes a "timely response." One month? Three months? Any guidance would be much appreciated.