I think it’s the OP’s wording that has led to mirth - “how we are supposed to arrange ourselves”.
I mean it’s quite obvious how you can.
But I agree it isn’t ideal.
I have children of different sexes, with a big age gap - dd16 and ds10. With the best will in the world, they ain’t going in the same bed!
So yes, if I were in a couple with children of those ages, it would mean one parent shares with the child of the same sex, but a lot of people don’t want that as children are notoriously not considerate sleepers!
I am on my own so would be less of a big deal - up until recently I’d have shared with DS in that situation.
But now DS, the youngest, is 10, we’re at the point where I’d be thinking “maybe i should share with dd instead” as the same sex. But then it would seem daft to have a 10 boy in a big bed to themselves whilst two women squash up.
So I can see how it still wouldn’t work for us, and just having individual beds for children is better.
The premier inn is good for that, but then tbh the child bed is a bit small and rubbishy for a child much older than 10. I think they may be starting to do twin rooms at PI, so if they do one of those as a family room it would be fab.