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Please see these topics: http://www.eng-tips.com/viewthread.cfm?qid=347923 http://www.eng-tips.com/viewthread.cfm?qid=1734 Thanks.

You need to provide expansion joint at podium near to all three tower and analyze them separately. Because each tower has different time period Based on there geometry and loading so the lateral forces will be different

For accidental torsion, podium would share a common diaphragm so you need to consider it as one but levels above podium where buildings are isolated, you should consider individual buildings and individual drift limits. You can search the forum. There is an ETABS manual posted sometime earlier on high rise buildings design. You can let ETABS do it for you. There is a tutorial available about it as well. See first tutorial here: https://www.csiamerica.com/products/etabs/watch-and-learn Thanks.