Hmm... I think the only ones I can think of is either one of the joggers that add a seat like Phil & Ted or Baby Jogger or Valco which both allow for a toddler to attach to the main seat as well (both on top as opposed to bottom like P&T). They aren't necessarily lightweight but because they turn into a single as needed it may be a good option.
And otherwise there are the sit'n'stands. We have the Joovy Ergo Caboose which is the heaviest of them all at 30 lbs but I love it and have used it as a single as well. The rest of the sit'n'stands are fairly lightweght... the Mia Moda's are getting good reviews.
Re: Dbl stroller rec. for 2yrs/newborn
Hmm... I think the only ones I can think of is either one of the joggers that add a seat like Phil & Ted or Baby Jogger or Valco which both allow for a toddler to attach to the main seat as well (both on top as opposed to bottom like P&T). They aren't necessarily lightweight but because they turn into a single as needed it may be a good option.
And otherwise there are the sit'n'stands. We have the Joovy Ergo Caboose which is the heaviest of them all at 30 lbs but I love it and have used it as a single as well. The rest of the sit'n'stands are fairly lightweght... the Mia Moda's are getting good reviews.