My Ride and Sure Ride puzzling?

I'm wondering if these 2 seats might puzzle together, either both rf, or 1 rf, and 1 ff. Currently in my moms car, we have 1 of my nieces, 2y 8m, rf in a my ride. The other one is 6 weeks, and in a flex loc. She's good there for a while. The 2 year old has maybe .5-1 inch left rf in the my ride (tall torso, I got them matching pajamas that I was putting away for later, she wore the 3T shirt from her set, with the 12m shorts from the baby's set). I was thinking about maybe getting her a sure ride, which I am assuming gets her more rf time, and the baby could have the my ride when she outgrows the bucket. The 2 year old is only 28lbs, and Is maybe 35.5 inches. Fitting next to each other is preferable to allow someone to sit next to them, however uncomfortable, if necessary. If they won't fit together rf, I could always turn the older one when the baby needs the convertible.
I might be able to try other things out if they buy more rf time, I can try them in a physical store (but I can actually purchase online) and they come in pink. She likes her pink seat, she likes that the baby has a pink seat, and I don't think she'd be happy if I took away her pink seat and didn't replace it with pink.

They don't puzzle well in any combination. The MyRide puzzles well with the Radian, but that's pricier than the SureRide. What's your budget? Are there any other convertibles you or the parents own that you might be able to use in your mom's car instead?

Darn! My sister (the one with the 2yr old.) Has a MyRide in her car, and I think in my BIL's car she has a Scenera. My mom of course hates the Scenera. The baby only has the flex loc. Is 2 Surerides next to each other with one rf out of the question? The my ride can always go to my sister's car. No matter how we do it, when the baby outgrows the flex loc, two seats have to get purchased (for my mom's and my sister's car). I could also go with a combo seat, but if there is some way that buys rf time,I'd opt for it first. As for other seats, keeping it in the same price range as the my ride is preferable.