It seems to me that to make this game successful, then each of your immortals has ONE unique skill, for a total of 8. That leaves at 7 other skills up for grabs that ANYONE can max and do all the skill challenges for and have a ball with.
For example, in my dynasty (called the Immortals...I know, no creativity there...), I have planned it as follows:
Gen 1 - Adrian (Logic)
Gen 2 - Brandon (Guitar)
Gen 3 - Carolyn (Writing)
Gen 4 - Dylan (Fishing)
Gen 5 - Evelyn (Cooking)
Gen 6 - Flynn (Charisma)
Gen 7 - Gwyndolyn (Athletic)
Gen 8 - Harmon (Painting)
That leaves Gardening, Martial Arts, Sculpting, Photography, Nectar Making, Handiness and Inventing up for grabs! If you can't keep your Sims busy with all that, not to mention television, video games, foosball, VR goggles...
I don't see anyone getting bored. If anything, there are too many options.
Edit: After reading everyone's following posts, I decided to let Harmon max Inventing (so that all my other Sims can use that easel if I want them to. Paining is fun!) He's going to be self-employed anyway with Descendent of Davinci LTW.