You cannot "get" both properties, but you if you already have the Megaton house (& even if you don't), you can use the Tenpenny suite as if it were your own by entering & exiting through the window of the room which is accessable from the outsie of the building.
You obviously cannot use the pipboy trophy display unit in two locations at once, & you will never be able to open the front door to the suite. Only through console commands.
If not on PC then the only way is to get lucky and hope the game will glitch and the room the player can stay in tenpenny tower will have the balcony doors open. happened to me so i had both houses.
why does it matter
Disarm the bomb and get the Megaton house, then go to Tenpenny tower, get inside, and talk your way past the guard to Mr. Tenpenny. Go out on his balcony, ignore him, and run around the side and you can get into the suite from the balcony doors. The storage is safe, you own the bed, and the robot butler acts as if you live there. You can't use the front door or buy custom themes, but otherwise it's yours. This may have been fixed with a patch recently, so make sure your last update was from a few months back.