If you are fluid bonded with the other person, sure no problem.
If not, the Ina 2 is waterproof, so it could be soaked in a dilute bleach solution (10%, meaning 10 parts water to 1 part bleach) to be sanitized for sharing.
The original Ina is not waterproof, and so it cannot be soaked in a bleach solution for sharing.
Hope this helps!
Here is the Materials Guide Index.
On there you can find out how different materials can be cleaned. Under the Plastic entry, they also mention that plastic can be wiped down with isopropyl alcohol to sanitize it.