Yes, i think ask for a comprehensive cognitive assessment and the gp to refer to continence. Gp also needs to look into cause for itchy legs, could be liver disease. I think you also need to refer to adult social care for a needs assessment. You can request this online or ring up. Look for your county council adult social care online.
Someone i know hasnt yet got the diagnosis of dementia (but they have ischaemic brain disease which can lead to vascular dementia), there is loss of inhibition (talking about poo when they never would have, watching a horrifically violent film with sadomasochism and sex scenes - stig larrson 🫣whilst workmen are trying to fix something in the same room), and a loss of known routines (washing hands after toilet with soap) and apathy....... So no real understanding of why something is wrong, no shame, no embarrassment.
I think in this case, the needs assessment by adult social care should confirm that their safety at home is in question, lack of insight into risk to selves and others through smearing of faeces, inability to clean up themselves and their own home i imagine also. So he definitely has care needs. Im sorry this sounds very difficult to cope with. I vomit quite easily with smells and have been known to stuff ripped up boots cucumber face wipes up my nose to try to cope.
In the meantime, the disposable gloves are a good idea. Maybe ice lollies might work or soup, to get more liquids down.
Maybe ask the gp if it woukd be sensible to relax the high fibre diet and switch to low residue diet, just till this issue can be better managed, as this would reduce the amount of times hes needing to poo.