If 2 teams play at the same venue then when you create a schedule you don't want them both playing at home at the same time. For example if you have 2 teams "Valley A" and "Valley B" that both play from the venue "Valley" when you develop your schedule whenever A plays at home then you want B to be away (road) and visa versa.
If you are using the Template Scheduler then this managed via a pairing system. It doesn't use the venues of the teams. Create you team pairs in the "Venue Sharing" step. This could be teams in the same division or in different divisions.
If you are using the Advanced Scheduler then make sure both teams share same venue and not a duplicate venue, the advanced scheduler will never double book a venue. To check the venue / teams setup: click on MANAGE on ADMIN HOME next to the division. Edit the team to change its venues.