In the second case, the wife asks the husband to use the condom, and he does. By her request, is she now guilty, and to what degree?
First, for those who may not understand about what we speak,I would prefer to lay the foundation for mortal sin before we begin, that is:
1. Grave Matter
2. Full Knowledge
3. Deliberate Consent
I would also add that the effectiveness (or lack thereof) of condoms is known.
I would also like to assume, for brevity, that both husband and wife have full knowledge, although we can modify this later, if necessary, as I'm sure you are more than familiar with these topics.
I would say that if the wife knows that her husband has this disease and is likely to contract it by engaging in the marital act, a refusal to live a continent life may most likely be a grave violation of the 5th commandment, a mortal sin, objectively speaking. It may also be mitigated, it seems, by factors such as age and the possibility that she may die of natural causes before the onset of the disease, if contracted during the course of a natural marital act.
Having said that, in response to your first scenario above, if the wife has knowledge that her husband is doing this and does nothing to prevent it, it would appear that she would be objectively culpable - again if the standards above are applicable. Primarily, both are engaged in frustrating the marital act and closing it to life.
If she is unaware of his disease, and unaware that he is using a condom, she incurs no culpability whatsoever. He, however, would be committing grave sin, objectively, regardless of his intention, however good it may be. He is frustrating the marital act, deceiving his wife, engaging in an immoral act (use of condom), and possibly infecting his wife.
If she is aware of his disease, and unaware that he is using a condom, of course, she may or may not incur some culpability. He, it seems, would be committing grave sin, objectively, primarily by using the condom and frustrating the marital act.
In the second case, the wife, knowing the husband has a deadly transmittable disease, asks him to use a condom for protection and knowing that this is grave matter, objectively commits a mortal sin. She is asking him to commit evil (use of the condom) to achieve a potential good (avoidance of disease), which is not acceptable.
There is little difference, as I see it, in using a condom for protection against AIDS or other deadly diseases as it is playing Russian Roulette.
I understand completely how difficult this must be for those who find themselves in this situation. I would take great courage and strength to live a continent life, particularly in the couple were younger.
I hope this helps, although I am certain that many will find that this is just too hard to accept. We are called, not to confirm others and ourselves in our sin, but to proclaim the truth, however difficult it may be.