Nota: Temos o prazer de responder a perguntas em inglês, ou numa das nossas línguas nacionais. Obrigado.
It will be impossible to visit all three towns in one day in January due to short day light. Skip Interlaken, it is not worth a visit. For a day excursion, I suggest to visit Mürren, with a stop at Winteregg.
I suggest to look at a Saver Day Pass which is currently at CHF 52.00, full fare (1/1). It covers all the public transportation to either villages: Grindelwald, Wengen, Mürren. You must buy it online in advance, the cost is increasing the higher the demand, and they can sell out as they are limited.
The reason why there are different amounts displayed when researching connections is because the initial cost displayed is a “from price”; it is the best offer in terms of costs yet comes with a few restrictions; it is often a Super Saver Ticket for Half Fare Card holders; it is not recommended to buy a Super Saver Ticket for day excursions because Super Saver Tickets are bound to specific train connections and do not offer any flexibility.
A Swiss Half Fare Card is worth the money if you are staying multiple days and/or you will spend at least a total of CHF 240 on public transportation tickets.