I am looking for a tandem pushchair for a tall toddler and a newborn. Can you recommend one please ?
Honestly, there is no ordinary tandem pushchair I would recommend to be easy to push as well as space-wise for a tall toddler + a baby. They get very bulky, also very hard to lift because of the center of gravity being bad with such a weight difference and one-behind-the-other setup... And most importantly, the double tandems have smaller seats, often MUCH smaller, so you need to be ready for your older one being tight in the seat, unfortunately.
One solution I would go for however, if a tandem is really a must, would be a bench seat that can be found on the Baby Jogger City Select Lux as it can accommodate even a really large child. The [[quinny-hubb|Quinny Hubb] had that too but is not easy to get anymore (even the normal seat unit of the Hub is on the larger side btw).
Apart from that, perhaps try out (really try out before buying) the Uppababy Vista, which's seat is not that horrible, but. the push comfort and the bulkiness may give you a bit of trouble.
My best advice here would, however, be a side-by-side pushchair (like the Valco Snap Duo), longevity-wise - based on my experience.