Hello,
Obviously the first step is to transfer the two gedcoms from GR to your pc. I would then copy them to another folder just in case you alter them incorrectly and need to start again.
The second step is to install FTM2012 so you can start practising with it and learning how to go about things. I use Legacy but all these programmes are quite similar in use. Once you have installed the programme you should see a folder where gedcoms you wish to import to FTM should be placed. With any luck you will find a dummy gedcom or tree, created by FTM, just to get you started. If there is then have a play around with it just to get the feel of your "new toy"

. If FTM asks if it should create new RIN's when you import, then say yes for later ease of counting the records.
Some people prefer to have a tree for each family, others like my sister and I prefer to have one joined tree because the more we delve the more we find unexpected links. For example, our mother and father were very distant cousins and that would not have been apparent if the lines had not been in one tree.
So, if you want one combined tree only:
Step 3. Read FTM's instructions on how it merges two gedcoms and either print out relevent points or make your own notes about things you feel are most important for you.
Step 4, import one gedcom into FTM, making a tree according to their format.
Step 5, import the second tree as a merged tree. Normally the only duplicated information you should have is that of you and your wife. Legacy analyses trees we want to merge and gives a list of all people it thinks are duplicates. It is then up to us to decide if the information is a duplicate or a new person for each case.
Step 6, re-import both gedcoms as stand alone trees (with new and succinct names) so you end up with three trees. FTM should give you the possibility of displaying two trees at once, side by side. Here you compare the new merged tree with each of the stand alones in turn for your and your wife's sides. This is just to check that everything has gone to plan. At the same time you should check the total number of names in each tree as well as the total marriages. The total names in the merged tree should equal the sum of the names in the single trees less two (as you both appear in each separate tree) and the marriages should number one less in the merged tree if my maths is not up the gum tree.
Step 7 treat yourself to a stiff tea and walk around with a smug grin on your face for succeeding. And if you had any bugbears to overcome perhaps you could share them here for future reference.
cheers and good luck, falcybe