Disabled Potential Beneficiaries

I have been approached to make a will instruction from a terminally ill person whose spouse has dementia and one of his children has Down’s syndrome. The testator is the primary carer and receives benefits on behalf of his son. I am minded to advise him to effectively disinherit his wife (including severing joint tenancy on their home) and leaving a third of the testator’s estate (he has 3 children) on a discretionary trust with the disabled son being the sole potential beneficiary.

In respect of disinheriting the wife, i am aware this creates issues under IPFDA 1975, and in respect of the disabled son is it more appropriate to create a Disabled Person’s trust on the testator’s death, although this may negate the benefits to which the son may be entitled.

What is the best way of approaching this issue ? Is there anything I have missed ?