Sorry for your loss. Does your UK family understand your immigration situation (and are they sympathetic to it)? If so, and if you and your lawyer determine there's no way for you to leave the US without severe consequences, perhaps the relatives can set up a simple video link at the memorial via Skype or similar. While it would be a poor substitute for saying good-bye in person, if there's no other option it would at least give you a way to experience the service as it is happening. Best of luck.