I'm not sure how to get the actual records - or if they even exist any longer - but if you think that the person died at Overbrook, you can contact the Township of Cedar Grove to get the death certificate - that way you can at least get the cause of death and where they're buried.
You just have to fill out a non-genealogical request form and send a copy of your ID, a $10 check and provide proof of relation (no extra charge):
http://www.cedargrovenj.org/site/index.php/municipal-service...It takes about 1-2 weeks to get it.