You really need to licenses. You are allowed by the license to install Lightroom on two computers. But the installation is for the personal use of the owner of the license.
Interesting. We do much of our photography together - almost all in fact.
Without bending anyones nose could the owner be Mr and Mrs?
Under the terms of the license, it wouldn't matter if you were legally married:
2.1.3 Portable or Home Computer Use. Subject to the restrictions set forth in Section 2.1.4, the primary user of the Computer on which the Software is installed under Section 2.1 (“Primary User”) may install a second copy of the Software for his or her exclusive use on either a portable Computer or a Computer located at his or her home, provided that the Software on the portable or home Computer is not used at the same time as the Software on the primary Computer.
You can find the license for your country in /Applications/Adobe Photoshop Lightroom 5.app/Contents/Resources/AMT/Legal.