With this in mind I only looked at people born in Ireland and I did come up with one group of people that both trees have in common and whats more they come from the general Co. Cavan area. Unfortunately of course those who are recorded as still alive have their identy hidden from me. Is there any further I can go before I try and make contact with persons B & E?
If you can find a married couple who are common in the Cavan trees, you can build a tree down from them as far as you can go. When you do this, you might be able to work out who the living people are. Even if not, it at least should narrow down a more recent family group that your wife's father is part of.
The same applies for the people in the US. If you build a tree downwards from their common ancestors, then remove the lines that went to the US, you should be left with a family group that stayed in Ireland and related to your wife more closely.
Also, if you've identified the common ancestors in several trees, you can try searching for them in Ancestry's members' trees. These aren't always the most reliable sources of info but some people do a good job and you may find a lot of leg work has been done for you already.