3 Across in Kia Soul

Hi! New here and hoping for some advice/recommendations. We are expecting our tax return back and are hoping to get some new seats for the kids. Currently our DS is 21.2lbs, 26.5" and will be 12 months on Saturday. He is riding in the middle in a Britax B-Safe. Our oldest DD will be 8 in April and is riding outboard in a Graco Turbobooster with the back removed. She is 59lbs and 52". Younger DD is 6.5 and 45.5lbs and 48". She is also in a Turbobooster but with the backs. I was never crazy about the Turbobooster but we needed new seats in a pinch and they worked. They seem so hard and uncomfortable! Anyway, since we are going to be moving DS to a convertible seat, I'd like to get them new boosters as well. I was reading that boosters with LATCH might be a good option since we are often riding with DS without sisters in tow and in case of an accident, their seats would become projectiles. I was hoping for any seat advice I could get. I was thinking either a Chicco Nextfit or Radian for DS and maybe two LBB for DDs? We would like to ERF until at least 3 and with the in and outs of all the car trips, I am considering moving him outboard. Or maybe not depending on how easy it is for the girls to buckle with the car seat configurations. I'm hoping that the seat we get DS will last until 4-5 and that these are the last seats we'll need for the girls but I know our car limits our options. Any advice is so appreciated!

I would do a Harmony backless or Incognito (if she is 60lbs) for the oldest, Radian for the youngest and a narrow high back for the middle.. We have a Frontier 85, harmony backless and Oobr in the back. I have also had a Frontier, Radian (get angle adjuster) and harmony backless. You will not be able to latch boosters and make a 3-across work. There is not enough room. We have a 2010 Soul.