how can two apple id's share the same ipad?

No, an Apple mobile device is designed for a single user at a time. Even if you did want to share by signing in and out you would need to erase the device between each user having a turn or risk having your content mixed up.

You cannot. The iPad does not support multiple users in that way. We’ll, you could factory reset it and then switch apple IDs any time you went back and forth…