Is a Rail Pass(Twin) better than point to point if we arrive in Frankfurt then go to Bacharach(and area), Baden-Baden, Colmar, Heidelberg then to Berlin, where we fly home
Check on of Rick Steve's rail sites and point-to-point map. Frankfurt to Bacharach is probably cheaper using point-to-point. I would use the Rail Pass (Twin) for the other trips. However, its sometimes a lot easier just to purchase the Rail Pass for the entire trip. It may cost just a little more, but it safes time and worry. Have a good trip.
Check out the prices on this site:
Here's a little more information on how to find the best fares on the German Rail site given by JB. After you get summary timetables for a particular route, click on the arrow to the left of each departure time to see the connecting points. Fares will not be shown for legs that ae solely within Switzerland. You can get fares for those legs on the Swiss Rail site. However, the DB site will give you fares for legs that either start or end in Germany (like the Basel-Heidelberg leg for a Colmar-Basel-Heidelberg route).
If you can commit to specific departure dates and times and book well in advance (up to 90 days allowed) on the DB site, you can get a Savings fare of 29 EUR for Bacharach to Baden-Baden, 19 EUR for Baden-Baden to Basel (enroute to Colmar), 29 EUR for Basel-Heidelberg, and 29 EUR for Heidelberg-Berlin.
If you can get discount fares, point-to-point tickets will be much cheaper than a railpass.
One other point to mention about travelling with a Rail Pass, is that these do NOT include the reservation fees which are compulsory on some trains (usually the high speed trains). You'll have to pay separately for these.
Frankfurt airport Regionalbhf to Bacharach is a local RMV ticket, available from an automat or ticket counter for €10 per person.
Bacharach to Baden-Baden: Use a Rheinland-Pfalz-Ticket, an all day pass for regional trains in the state of Rheinland-Pfalz, purchased from the automat at the unmanned Bacharach Bhf for €27 for both of you, to get to Karlsruhe. From there it is a local, €5,20 pP, ticket to Baden-Baden Bhf via regional train or S-Bahn.
Colmar is in France, a German Rail pass would only get you to Kehl, across the river from Strasbourg. You'll need French Rail tickets from there. Point-point tickets from Baden-Baden to Kehl are €8,40. Actually, you can probably purchase tickets all the way to Colmar at the B-B Bahnhof. If you want to get to Colmar via Basel, purchase a Baden-Wuerttemberg-Ticket for €28 for 2P. It will take you to the Badbahnhof in Basel, Switzerland.
To get back, to Heidelberg, purchase tickets in France back to Germany (Kehl), then use a Baden-Wuerttemberg-Ticket (€28 for both of you) to Heidelberg.
For Heidelberg to Berlin, your best bet is a Dauer-Spezial-Ticket purchased in advance from the Bahn website for as little as €49 for two. This ticket will use high speed express trains like the ICE.
Buying Laender tickets as Lee suggested will get you better fares than the ones I suggested. And they don't have to be purchased in advance. For Heidelberg-Berlin, be sure to book as far in advance as possible. The special fare of 49 EUR for two is a whole lot better than the standard fare of 116 EUR/person.