A single pivot is fine. Two pivots would not be my choice, particularly under hard braking. Also the weight is substantial. My tandem/tagalong picks up speed downhill very quickly. Uphill is basically anaerobic threshold workouts!
Btw, my two are much older and bigger than me, those are two of my nieces. Buy a kiddyback when the first is about four, you’ll get 6-10 years of use, then you can sell it for what you paid.
I always wanted a Haze Pino, well actually I wanted a Bilenky Counterpoint Opus, but they were just far too much money (still are). Circe make an affordable option now. Thorn are the go to for kiddyback. Mine was one of the last Dawes twocans made. They do come up on ebay and the tandem group facebook page. I paid about £500 new plus another £300 in modifications and a further £200 for the Burley Picollo (since sold).
And the law states that a bicycle for multiple occupants must be adapted for such. Sitting on the back of a cargo bike doesn’t count (unless you add child seats). But there is no limits to how many you can add!