No. PIP is not a work-related benefit, although it can be taken into account if you have a motorbility car and want access to work to provide funding for transport to/from work, but that’s not a given.
PIP is there to cover the additional costs which relate to having a disability, and these can depend on the disability you have.
So for instance I have a visual impairment, buying a screenreader for my personal laptop is an additional cost. Having to sometimes get cabs to/from destinations where public transport is not available is an additional cost which would be covered by PIP.
But adaptations for my job would be covered by access to work, although the government is cutting that back to the bear bones and it’s not being made public knowledge so the government are in fact making it harder for the disabled to remain in work but that’s a different discussion. But in my personal case my employer have covered the cost of my adaptations.
WRT whether CMS should be taken from benefits, it’s a difficult one as it would be the primary caregiver who receives any child related benefits so it’s a grey area. That being said, I do think that benefits should be taken into account on both sides.
Disability benefits are one which you need to tread carefully, but unemployment benefit should be taken into account with regards to paying CMS.
By the same token, IMO if you’re receiving CMS this should also be taken into account if you’re claiming benefits. Because while for some it is minimal, there are certainly people who do receive CMS to the tune of a few hundred pounds every month but this isn’t taken into account and they still receive maximum benefits which is hardly fair.