Ex-pats entitlement to sickness benefits

I’m looking for some guidance if possible, please.
My client (61), a British citizen, returned to the UK in late 2017 with a Dutch sickness benefit (WIA) in payment of approx. 1500 Eu per month. This was recently drastically reduced due to an overpayment and he is now struggling to pay his rent. He has severe COPD and is currently shielding. He has had 3 jobs since returning, one of which lasted for a year, but each time has had to give up because of his health. I have identified a potential PIP claim and possible NSESA, but am having second thoughts because of competent states and the payment of the overseas benefit…
He has, as I see it, an “independent right” to claim NSESA (I think he just meets the NI con criteria) and meets the 104 week rule for PIP. Am I barking up the wrong tree and what possible pitfalls are there in pursuing these claims.
Guidance much appreciated. Thanks.

So, to partially answer my own question, I think I can probably rule out NSESA as even if an overlap is provided, the WIA is by far a more generous amount that NSESA, so as both are “insurance” benefits, it appears he can’t get both. As PIP is not an insurance related benefit, I’m not sure about this