Renovating pond and stream please help with advice

My parents purchased the property years ago and extremely overgrown after pond builder/prop owner passed away. I'm trying to come up with a plan to rehab the pond, dam, stream to its former glory and an idea of what maintenance weekly, yearly, etc should be done. As the are getting older they really want their grand kids kids to be able to enjoy this joy as well. Any help would be great. I have started researching but this seems like a one of a kind setup. Thanks