I say let them be there, if they wish, as long as they don't get in the way.
However, from my personal experience, I would NOT want to be present to see a family member of mine being resuscitated and can't understand who would want to. Unfortunately, a little over a year ago, I had to leave work and go to the ER (in the same hospital) because I was told that my Mom was sent there. I was scared; I didn't know what was going on. When I found her and saw her unconscious, my world came crashing down. When the Rapid Response nurse identified who I was and told me she had coded upon arrival, I broke down. Even though I wasn't there, since I have seen how CPR goes and knowing that my dear Mom went through that tore me up. They got her back, but she was only with us 6 more days until I lost her. I can barely handle a code now, even when they aren't mine. I nearly had an anxiety attack last week after just seeing the Code Team; I didn't even see the patient. It brings back sad memories. I thought I had healed some, but apparently not.