I forgot to ask you about budget. What are you looking to spend overall or per seat?
For the oldest, they are over the height limit of most boosters, but the Safety 1st Incognito (if you can find one) goes to 60” and the Diono backless goes to 63”.
For the 8yo, you have time before they outgrow the common 57” height limit most backless and high back boosters. You’d have pretty unlimited options there unless a HBB has too low of a belt guide, so you should be able to find something that fits.
The youngest being in a harness or a booster is a call you’ll have to make based on their maturity level. A harnessed seat can be easier in a 3-across because it leaves more space for the booster riders to buckle. Some narrow combination seats include the Graco Tranzitions, the Chicco MyFit, and maybe the Evenflo Maestro.
In general, try before you buy if you can, and if not, order from a trusted source with free returns!
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