Start by going into your profile which you do by clicking on the icon down in the bottom right of the screen. then go into your settings as shown by the arrow in the image.
on your options page scroll down past Terms of service in the first image to share settings shown in the second image of the collage.
Go into Facebook. I disconnected my account for these walk through photos but yours will have your Facebook ID shown next to where is says Facebook if you are already connected.
So you have clicked on Facebook and you will see this screen. Click on the 'Share to' option and uncheck Timeline. You may have something pop up asking you to authorise Instagram to manage your page/s, if you allow this your pages will then appear as checkable options below timeline ( last image ).
Check the timeline you wish your Instagram photos to feed to and you are done.
Then take a photo and test it out!