Ive tried many, many, many carseats.. you can say Im a bit obsessed with carseats (not really I just aren't afraid to change if needed). Right now I have
My 7yo in a 5pt harness Frontier FF combination (FFing to booster). This seat lasts FOREVER but is only FF so not good for a older child who has outgrown RFing carseats. I do love it though. My oldest is a figgets a lot in the car and a booster just isn't safe for her, she moves the seatbelt around when in one. My oldest loves this seat!
My 5yo in a 5 pt harness Natalius. I hate, hate, hate this carseat. It was suppose to be replaced but I realized my son's carseat was a month from expiring and replaced his instead. This is a FF combination (FF to booster) but the buckle sticks no matter what we do. Its being recalled so I have to call the manufacture for the new buckle for it. Honestly, when we have the funds Im getting a frontier for my daughter.
My 3yo is RFing in a Radian. Love this carseat. By far my favorite. Its pricey but so worth it! He actually wants to go on car rides, which is unusual since he hates sitting still, just because he loves this seat so much.
My 16 mo in a Graco MyRide, RFing. Im 50/50 on this seat. Im not a fan, buckle issues again. Also, the bigger my baby gets the more uncomfortable she seems to get. However its easy to install and worked well in the seat combination we had in the back of the van when the baby was born so it worked for us. She is 3rd in line for a new seat. I have to get the baby a seat first, then my 2nd daughter then her. Hopefully before we move in November everyone will be happy in their carseats.
Im expecting in Sept. We don't know if we will just go straight to a Radian or get a bucket. We are moving to where its extremely cold so I was thinking it would be nice not to have to get a newborn into a carseat in the car when its like 0 degrees outside. If we get a bucket we will probably get a Keyfit 30.
BTW I LOVE that you are concerned for your grandchildren safety! My inlaws and father aren't allowed to transport the children anywhere because they don't see a need for carseats. My FIL told me I could give them to him if I wanted but he refused to use them. I love it when Grandparents get themselves informed and do whats best for their grandchildren.