Hmmm, tough question. I would be surprised if it fit the pram to be honest. There are so many toddler seats on the market and most of them are designed to fit the one type or brand of pram and that's it.

Even if it did fit I'd be concerned about weight restrictions (they are stated on the pram and toddler seats when you buy them), the possibility of the weight not being distributed evenly between the toddler and the baby, the seat not clipping into the pram properly and various other safety concerns.

I'd be more inclined to look for a pram and toddler seat set on eBay or in the Trading Post, etc than putting two randoms together and hoping for the best.

Good luck!