Car seat recommendations 16 month old - 5 yrs?

My kids (5 years and 7 years) are both in Diono Radian. The seats are narrow enough that I can sit between them in the back seat when needed. We have them using the 5 point harness, and they are able to buckle themselves in and out now. The weight limit goes up to 100 lbs, but my daughter is only 45 lbs, so we won't will hit the limit before she's 8 and doesn't need a car seat at all. We bought these once they outgrew the baby bucket seats, and had them rear facing at first and turned them around at 2.5 years. 

Note- these seats have steel frames and are heavy! However, as the kids were bigger and could walk on their own, I've rarely taken the seats out of the car, except to remove the cover and wash them. They were more expensive than the plastic seats, but I love them because they were narrow (you could fit 3 of these in a back seat if needed) and extremely durable. I decided on these also based on high praise from my friends with older kids who used them from infant to 8 years old on their kids.

I use the Graco Slim fit 3 in 1 convertible car seat. I like it and daughter likes it just fine. I have heard good things about the graco extend 2 fit as well.
I can only imagine how you are getting a 16 month old toddler into an infant car seat! Wow! We had the same chicco car seat. They are only supposed to be used until the baby is 30" tall maximum. Then you switch to a rear facing convertible car seat. They stay rear facing until at least 2 years old or at most 40" tall. My daughter is 2 yrs 3 months and 37" tall and I had to turn her front facing, her legs simply did not fit rear facing anymore. But the Graco slim fit we are using is working fine front facing as well.

Hi!
now it is increasingly recommended to keep children rear facing as long as possible.
So taking that into account I maid my research for my now 2 years all so I will recommend that you search the ones that can be rear facing until 50 lb like
Cybex Sirona S
NUNA exec (this is the one I bought)
Graco Extend2fit (they have different models)
Britax One4life
Diono (I can't remember the model)

I don't know if other brands have also can be rear facing until 50 lbs but this are the ones I like a few months ago

We liked our Clek Fllo. Used it for over 6 years through two kids. Our kids are average sized and were able to rear face comfortably until they were over 5 years old. Then our younger child forward faced in that seat for another year and a half and went straight to high back booster just before age 7.

We loved the extended rear facing and that the seat was extremely narrow so we could get 3 seats across when needed. We were also pleased that the seat got us to booster age.

We have the Nuna Rava and I really love it. Every time I need to install it, or adjust it because my son has grown, it's so easy. One of the reasons it is supposed to be safer is because car seats are frequently installed incorrectly, and this one is just so comparatively easy. I had to take it out and install it multiple times recently when we moved a bunch of stuff, and I was so happy to have such an easy car seat. The fabric is really plush and comfy, and also machine washable, which is really helpful when your kid has pee accidents in the car after they're out of diapers. The smaller Clek was the other model we almost got, because it's supposed to be really safe, and it's not washable. My neighbor had it, and hers was covered in melted crayon, and that sealed the deal for me. The Nuna Rava fits rear facing until about 5 years old, which our pediatrician recommended. It is also a smaller model to fit in smaller cars (we have a Prius and the front passenger isn't totally squished with rear-facing), though I don't think it fits 3 across in most cars (there are other models that do that). It doesn't do anything fancy like rotate, but it has these little slots you can put the straps in on the sides to keep them from getting lost under your kid when they're getting in. You can also change the angle of the seat back. 

There was definitely a phase our son went through when he didn't want to get in the car seat, and it can be really stressful for the parents, but it's totally normal boundary pushing for toddler kids. Our son is 3 now, and all I have to do is suggest that he looks like he needs help getting in, and he switches into "I want to do it myself!" and gets in himself. Janet Lansbury has some episodes on her podcast that talks about getting your kid into their car seat. I find her advice so helpful in general, and her carseat advice helped us through the phase of strong resistance to getting into the car seat. https://www.janetlansbury.com/?s=car+seat 

I recommend the inexpensive Cosco car seats. They are FAA approved, lightweight and easy to switch between cars and to use for air travel. All car seats must meet strict safety requirements so no need to buy a lounger! My kid loved hers. 

We absolutely loved the Nuna Rava--it's a tank of a carseat but easy to install, to clean, and reclines back a bit which was amazing for our son who would take naps in the car up until about age 4. Nicely padded and he didn't complain. Our son has always been very tall for his age and he stayed in this seat just about until he turned 5.

We also have the Diono Radian and other bonuses are: it is narrow enough to fit on an airplane seat (we used it on a trip to france) and yes, it’s heavy, but it has backpack straps. I’m a very small adult (4’11” and 105 lbs) and I manage it just fine in airports. One of the highest if not the highest ratings for safety. Pricey but worth it if you can swing it.