Hi. If you are using I devices on the same Apple ID then yes, the messages will sync. But that would also mean you would see her messages as well. The device would need to be signed in to Apple to do this.

No idea about android. Microsoft may do the same but never used their tec for phones or tablets.

Me:43 Her:42
M:14
S:9
EA started 2014/03 (or there abouts)
PA started 2014/05/30
BD:2014/11/05
I left 2015/10/01
I returned 2015/05/02
She left 2015/06/10
OM still on the go.