Question about FHA loans, but a bit different situation

[Daniel S.]

Situation:  someone owns a townhouse and decides to purchase another townhouse that is directly attached to theirs (but different mailbox numbers).

If they use an FHA loan do they have to move right next door otherwise it's fraud?
Could they move over and then move back if they "decide later" that they like their old home more?  How long until they could do this?

Thanks!