I can't help with the McLaren, but I may have a recommendation for Threehearts. I bought a Kidco City Light Double, which is a lightweight umbrella stroller with a high canopy that semi-reclined. I've used it for two Disney trips, the most recent when my 4-year-old was 40 pounds, 40 inches tall, and my 6-year-old was 50 pounds, 46 inches tall.
It held up well under their combined weight and was easy to maneuver. However, once they were sitting, the baskets were pretty much inaccessible. We attached small bags behind them to compensate. In the semi-reclined position, my oldest son's head did overshoot the back of the seat - but he wasn't sleeping anyway.
It was pricey at $219. But, I needed only two Disney trips to cover what it would have cost us to rent.