Hellobee Boards

1. Combi Shuttle
At 16.75 inches wide at its widest point, the Shuttle infant seat packs a lot of safety, installation, and comfort features into a small space: an anti-rebound bar for increased rear-facing safety, built-in seat belt lockoffs, easy-read level indicators, energy-absorbing foam-filled head wings. It holds infants rear-facing up to 35 pounds and up 33 inches and is a good choice for triplet or twin seating. Combi Shuttle, $179.99

https://blogs.babycenter.com/products_and_prizes/02052015-13-car-seats-that-fit-3-across-in-most-vehicles/

@HappyBaker: Also if/when you do have to upgrade the baby, you may be better off getting the 5 year old a booster or another combo seat and letting the middle child move up to the diono.

@2littlepumpkins: Doesn't look like it is that much smaller than some of the others. But such a nice looking seat!

5. Uppababy MESA
The MESA infant seat is on the pricier side, but the safety features are noteworthy, particularly the enhanced side-impact protection due to the head wings and a shell lined with energy-absorbing foam. But what really makes us love this one are the easy-installation features: auto-retracting lower anchor LATCH attachments which make it much easier to get a tight installation and a reassuring tension indicator on the base that turns from red to green to let you know when you’ve got the right level of tight. Another small, but nice, refinement: recline angle indicators on each side of the base, which makes installing the seat in a variety of positions a lot easier. 2017’s big update: The MESA is now the only flame-retardant-free infant car seat in the U.S. — its blue Henry/Blue Marl version uses only naturally flame-resistant wool as padding (it’s $50 more expensive than other versions, too). The MESA holds babies from 4 to 35 pounds and up to 32 inches; it’s 17 inches wide at its widest point and its base is only 14 inches wide. It’s a natural for 3-across infant seating for triplets or plays well with convertible seats. UPPAbaby MESA, $299.99

We dont have 3 across but the Mesa fits really easily next to our clek installed in the middle position rear facing. The car we use most often doesn't have enough forward/backward room for a rear facing car seat behind the drivers side.