Hmmm . . .
This is a little weird, but I would move in Serena Durwood and her son Zack. If the heir is a girl, the (fantastically handsome) Zack would be able to reproduce with her, or reproduce with female townies to make a few prospective spouses once he's older. Serena has a few points of Alchemy, which would come in handy when making Invigorating Elixirs for the Ice Personality challenge, and depending on what you're having Chauncey do she can garden or fish, and have Chauncey paint and sculpt. Zack, on the other hand, can be kept busy skilling up in painting and sculpting to take over once Chauncey dies.
Of course, Rick Durwood can also be moved in for gardening skill, but then you'd also have to bring Zoe and I don't see what she could do besides take up space, and gardening is easy enough with a lot of breathing space to skill. In addition, Rick dislikes Chauncey, which isn't a huge factor but might make things a little tense. Also, since Serena is (obviously) a girl, she could just invite her husband over and Try for Baby with him if you want a spouse for Gen 2, although I would beware of Rick's lovely ears.
If, on the other hand you were to go with the Ivy's, I'd recommend moving in Annalove and Peanut. Annalove, with her Gatherer trait, would make an excellent gardener while Peanut, with a level 2 painting skill, could take over painting. You could have him skip school for this, since artists generally make plenty of lifetime happiness points for a mid-life crisis. Again, you could move in Rainflower but then you'd have to move in Dreamer Ivy, too, which I can't see as serving any purpose. Chauncey could sculpt with Peanut taking over once he dies, and Annalove could reproduce with Rainflower for a spouse. I don't know what Peanut looks like grown up, but he's a cute kid so he might also be a potential spouse. Check out Sims Wiki for more.
In my opinion, the two families are quite evenly matched. I think it's basically a toss-up between Annalove's Gatherer trait, and Serena's witchery and alchemy skill, while the Durwoods can make quite lovely children but Annalove and Rainflower may have a better chance of producing a decent spouse. Overall, I'd go with the Durwoods as Zack really is a lovely young man capable of producing beautiful children (if you don't believe me, check out ombradellarosa's Callahan Life States Dynasty) and the alchemy skill can really be a lifesaver when trying to crank out 25 ice sculptures, with gardening generally being easy to skill up in no time with a large enough garden.
However, it all really depends on your founder's supermax and what you're planning to have Chauncey do., since you might not need a specific skill from your helpers. I hope this helped! Sorry about all the text--I'm kind of a long-term strategist. Good luck!