PIP is totally focussed on the extent to which someone can carry out the narrow range of activities covered by the form.
I strongly recommend you read some of the many sources of advice on completing the form, or invest £20 in the guidance provided by an organisation called "Benefits and Work". At the very least, Google "PIP descriptors and points" so you know what the criteria are.
If someone can't carry out an activity safely, repeatedly, to an acceptable standard or in a reasonable timescale, without prompting, supervision or assistance, they can't do it.
Each answer needs to spell out which of the medical conditions stop them doing the activity, eg "Because of depression, I have no motivation to bathe or shower and have to be prompted to do so".
Even when the form has been done well and there is loads of supporting evidence, applications are often turned down. This is why the number of successful appeals is so high - 80% or thereabouts (and that doesn't include the decisions that are overturned at the intermediate "mandatory reconsideration" stage).
I've had many clients who get 0 points at the first stage, but have gone on to get the enhanced rate of both elements at mandatory reconsideration/appeal.