Right Knee - ACL Injury. To be taken?

Hello, My father has met with a bike accident past 20days before (5th Dec), and got major fall on his Right Elbow & Knee. While we consulted with Dr & done a Xray, we couldn't found any major injury/bone frature in his Right knee. But when my father tried to walk, "he is able to stand on his feet but he says his ankle will get twisted suddenly, however he can lift his leg lying on bed". To ensure deep investigation, we done a MRI and then came to know that he has a ACL Complete Tear (as per report). Now since he is on bed past 20 days, I wanted to ask what should be my further proceeding on this? Is Surgery required? Is his age fit for surgery? Best time for surgery? Which method of Surgery is best? Does Physiotherphy can heal automatically? Precautions needs to be taken? Please let me know your valuable response on this. Attached Xray & Mri for your reference. Thanks in advance.