It would be best to start with a TV Fool report based on your specific location. The first report includes the warning, "WARNING: Address was only resolved to zip code level and might not be that close to your actual location. For more accurate results, try entering a specific address or coordinates." Please consider posing a more accurate TVFR.
Successfully combining two UHF antennas requires far more equipment than you might expect. The reason is, the signals from each will interfere with each other, resulting in less reliable reception from both directions. This is especially true when two stations are using the same channel.
I understand you don't want to use a rotator so I would suggest running separate coax from each antenna. Add an external tuner to the TVs that would need to be 'channel-surfing' friendly and A/B switching where the need to see both markets is only occasional.
http://forum.tvfool.com/showthread.php?t=2882
If your actual signal prediction is similar to that shown in the ZIP Code level report, I'd use a Winegard HD7015 aimed north at the Milwaukee stations. The 7015 offers enough gain to drive a passive 4-way splitter with no amplifier needed... One can be added if the need is proven.
The Chicago signals are quite weak (per the ZIP Code level report). I'd get very aggressive, using an Antennas Direct 91XG equipped with their CPA19 preamp. I'd also explore higher mounting options to see what improvement in signal strength may be available... Another reason to run a few new TVFR's.