How do we legally get it home without a license plate?
If the vehicle is purchased in Indiana and is going to be registered in Indiana, I don't think any of the temporary plates an individual can buy are relevant.
To be 100% legal, you'd have to trailer it or have the current (about to be former) owner drive it while his plates are still on it.
To be "probably going to be ok" you can take the license plate off another vehicle and keep your bill of sale in the car. Note that to be 100% legal, you'd need to have the bill of sale notarized with the date AND the vehicle the plate was originally on needs to be "disposed of" (traded in, sold).
You have until midnight of the date the title is signed to get the vehicle from the buying location to your place of residence.
You have until midnight of the date the title is signed to get the vehicle from the buying location to your place of residence.
You have 30 days to register it, when you go to the BMV they will give you a temp. tag to put on it until they send you the license plate.