I tend to simply walk to the very back of the platform to get companions to get on (The elevator in the Grove I sometimes have to do a little jig to encourage the last person to actually get on).
Of course, most similar games (Including Larian's prior game, Divinity 2) do it better by having formation settings so it's easy to manipulate positioning of companions. A feature that BG3 for some reason completely lacks (Which also impacts other aspects of the game, like positioning when starting combat or when traps exist and you don't want companions running through them like complete morons)
I'm not sure of the reason for it not being included in BG3, but hopefully they won't omit such a fundamental feature in future titles.
