They've already filmed Freed. Freed and Darker were shot at the same time and the budgets of each film were half of Fifty Shades of Grey. While Darker may not make as much, it will be a hit at the box office and hopefully, get better reviews than the first movie.
I've invested a lot of reading time into this series. Whether or not they are box office hits, will not make a difference to me. I will see them both very happily. I for one, am so looking forward to their release. As I've mentioned before, these movies are just for sheer entertainment. It's not like they are Academy Award contenders...and I'm ok with this fact. As long as most of the key parts of the book(s) are filmed, I personally, will be a very happy camper.