You definitely want to keep separate systems ... the core idea here is that you want a Next Actions list composed only of things you can do right here and now, so having your wife's tasks on your list will definitely confuse things.
However, there will be projects and tasks you both share.
For joint projects, brainstorm a list of actions together, but wherever possible, assign tasks to specific people. If either person can "Call Plumber" odds are it won't be done as quickly as if you know you need to call the plumber. Then "Call Plumber" goes on your Next Action list, and "Waiting on my husband to call the plumber" could go on her @WaitingOn list.
Joint projects should be reviewed once a week or so to determine next steps and assign new responsibilities. I suggest keeping a Weekly Review checklist (i.e. clean out wallet, clear physical inbox, clear email inbox) and include "Review projects with wife" on the list, so you're sure to get it done.
Enjoy!