Hi David!
First, I hope you had a terrific time at the "Wonderful World of Disney." Second, as someone who tries to get the biggest "bang" for his buck, I certainly understand the question.
Time of year has a lot to do with cost at Disney. Disney prices are always cheaper in the off-season, which is generally from early September-the end of March, excluding major holidays such as Thanksgiving and Christmas. If any of the proposed vacations fall within those off-season months, not only will it cost less but it's generally when Disney offer additional discounts guests can take advantage of. Not sure when the anniversary is, but definitely look for an off-season family trip, perhaps not during a major holiday.
If you're on a budget, and looking at 2 vacations within 12 months, you may have to make the trips shorter (approx. 3 days), and at least one should be at a Value resort.
In addition to the trip itself, you want to have some discretionary income for souvenirs, so it doesn't hurt to put a little cash to the side even now, anticipating a 2 trip investment.
You can click here to sign up for updates on Disney World parks, which generally will include special offers from time to time.
And don't forget, memberships such as AAA offer Disney discounts as well.
So to summarize: If you plan, keep abreast of special deals, and travel in the off-season, 2 trips within a year can certainly be accomplished.
Best Wishes, and hope it all works out for you and family!