I have a couple of suggestions -
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You can disable the Groceries target, by tapping the target number. This would allow you to continue using the target functionality but your spend in the Groceries category will still be deducted from the overall monthly target (it would probably make more sense if spend from disabled categories wasn’t deducted from the overall target).
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If you only spend in the Groceries target (I realise that’s unlikely of course), you could double the target number for that category.
Just to mention, bill splitting is one of the features that’re next up, according to the roadmap but judging by the name, it may only be available for the Bills category not the Groceries category 
@hugo there’s a couple of potential tweaks to the existing / upcoming features here so I thought I’d mention you, to make sure that you see this post