It is possible to fit 3 car seats in a subaru forester. I wrote a detailed post about it today. You should be able to put both your 3 year old and your 5 year old in the
Safe Guard Go Hybrid
Booster behind the passenger and in the center and fit just about any infant or convertable seat (including the
Britax you have)
RF behind the driver. The
radian would also work for your 3 year old. Both of these seats are 17" inches wide, which would leave up to about 19" for the
infant seat.
We love our subaru forester too and hope you can make it work! $400 on new car seats is a great deal compared to a new car you don't want!
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 | SafeGuard - Click for more info |  | Indiana Mills and Manufacturing (IMMI) is SafeGuard’s parent company, and has been in the business of developing and manufacturing quality safety systems for every facet of the transportation industry for over 40 years, covering everything from the heavy truck and agricultural industries to child seating.
IMMI has a world-renowned reputation for creating and promoting the highest rated safety harnesses and restraint systems available today, from integrated child seats in production vehicles to campaigning for increased use of safety harnesses on public transportation systems. Based in Westfield, Indiana, SafeGuard has been creating and testing essential components used across the child safety seat industry through their state of the art crash testing facilities since 1961. The SafeGuard and SafeGuard Go are IMMI’s first direct foray into the child safety seat market, and the results are simply outstanding. No other car seats or boosters are designed with as much attention to structural integrity, ease of installation, and total child safety. This seat has been subjected to the most thorough and extensive testing “ever conducted in the industry”: virtual prototyping with computer models; rigorous front, side, and rear impact crash testing; and environmental testing in a range of climates and road types. | |  |
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