For your situation, I'm not sure I agree with the wisdom here. The 5000 miles your wife has are essentially worthless on their own. Did I read you right that you and she will take two trips in the next four years? If so, her earning frequent flyer miles hardly seems worth it; I'd concentrate the mileage earning in the account with more miles. Transferring miles between accounts incurs a fee, as QueenOfCoach noted, and topping up separate accounts to have enough to redeem something useful is a somewhat difficult juggle if you have as little activity as you suggest.

Also, if you're planning to redeem miles rather than pay cash for most or all of your wife's travel, there's even less reason to worry about her account. If you travel more than her, it might make sense to pay for your travel and use the miles you earn for her travel.

Note that most posters here fly at least 50k if not 100,000+ miles in a single year, and many have account balances in the hundreds of thousands of miles. The calculations in those situations are completely different than when you're trying to eek out an award trip less than once a year and aren't worried about earning elite status.