One of the huge benefits of BI is that it's simple, you just give everyone the same amount of money. The more your start layering on exceptions, the more bureaucracy you'll create and you're back to square one.
The PwD piece falls more under healthcare (which I think should probably just be universal), so if their health-related benefits can be separated out, they would just get the standard basic income.
Retirees only need special consideration for political reasons, since social security may exceed basic income, but it could also be separated out into a supplemental amount to make basic income more universal. Ultimately they could converge to avoid special treatment.
And whether children get the same amount as adults is an open question among BI advocates; I don't have a preference either way and believe it should be studied empirically.
There should simply not be a 'PwD' element to BI - that should be a separate item altogether, otherwise it's just the thin end of the wedge. Leave it in healthcare-based welfare where it belongs, where both complexity is expected and health issues are better understood.