I've seen many people question how to get Shadow or Tails as you sex partner sooo
To get Shadow~
Leave the chao gardens and go to Eggman's base. You should find him sitting there in the BG. Then click on him while wearing the Amy Rose or Rouge the bat outfit, the click Sonic's mouth
To get Tails~
Once again, Leave Chao Gardens but this time go to Emerald Hill and you should find Tails in his Tornado. Click Tails while wearing the Cream the rabbit outfit, and then click Sonic's breasts.
Hope this helps you guys out some ^^