> 1. How do you specify the random effect for multiple variables? Ignoring age (see question 2), would this be correct?
> Rx effects: site (category 1-8), family_ID (continuous categorical), sib (factor)

Could you describe a little bit more about these 3 variables and explain why you consider them as random-effects variables? If you treat them as random-effects variables, they should not be included in the model specification because that is for fixed-effects variables:

-model "group*time+sex+handedness+IQ_PR+IQ_VC+site+family_ID+sib" \

> Age is both a within subject and between subject factor.

Do you mean that 'Age' varies within subject? Is this a longitudinal study? If so, yes you can do:

-ranEff "~1+age" \

3dLME is not so flexible in dealing with crossed random-effects. Alternatively a region-based approach would be much handy in terms of handling such a scenario: [afni.nimh.nih.gov]

Gang