Separating (1) children (2) people with disabilities (3) retirees and (4) other adults, is I would say an upper bound on complexity.
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.