Nearly everyone prefers to leave this world with other people having a positive perception of who they. And lots of older people, aware they are nearing death, plan types of activities similar to what you described. These are just facts.
Additional facts:
You are not under obligation. You may feel you are, or family may have the opinion you should go, but that's just their opinion.
You are an adult. You have the obligation and the responsibility to take care of you and your child above anyone else. Period.
You are an adult. You have the right to be with whom you want and not to be with anyone you don't want to be around. Period.
You have the choice to go, and spend the amount of time at the event that you choose.
You have the choice whether or not to allow your child to go, or not.
You can choose not to go.
And you can choose whether to make up and excuse for not going or to be simply honest.
I don't advise making up an excuse: dishonesty always has a chance of backfiring. If you say you're ill, will family press you to allow your son to attend anyway? How well will that go over?
If you decide to make up an excuse, what's the probability that some anxiety about making up an excuse will hang around your consciousness until you deliver the excuse, and maybe afterwards also?
If you decide to make up an excuse, will your father (or family) be prone to pressure you into seeing him and/or the video, and accept the "gift" of his life story at another time? If that's likely, then how will you feel and what will you do?
How does making up an excuse fit with your perception of your self as a mother and model the behaviors you wish your child adopts?
I can understand you not wanting to go; I certainly wouldn't want to. I suggest you plan something else you and your child can do that day, and simply express your apologies (and reason, if you have to):
