How can I remove residual adhesive that may contain asbestos from wood?
First, I agree with diceless, it is probably perfectly legal for the homeowner, to deal with this problem himself (assuming no part of the house is rented to a third party).

On the other hand, I agree with Mazura, you may be opening a huge can of worms here.  Since we are only talking about 2 bedrooms, I have to question the cost and time effectiveness of trying to rehabilitate the wood if the cutback contains asbestos.  I realize there may be problems matching the height of the bedrooms to the hallways or other areas, but if there is asbestos (and the floors are flat enough as is), just nail down new 3/4" hardwood or good quality 1/2" engineered hardwood over top of the existing floor.  Just use a heat gun to remove the excess cutback to ensure the floor is flat enough.

If the cutback does not contain asbestos, remove excess cutback and then go at it with a drum sander (rent it at Home Depot or wherever).  

If a home sale is in your future, I realize you may not really want to know whether the cutback has asbestos since if you do, you'd be obliged to disclose such on sale. But until you know, you can't really plan the right course.  You should be able to scrape up a sample of cutback, mail it to a lab and get results in less than a week.  e.g. http://www.asbestos-test.com/