Welcome to the forums Pedey.
There are three programs that we recommend for decryption of blu ray movies. Two of them are free, or have a free option.
DVDFab is a complete set of tools for decryption and compression of movies. When you download the trial for the program, all the different modules will be functional for a short time, but when the trial ends, there is still one section that will work to decrypt and rip your blu ray movies to the hard drive. That section is called DVDFab HD Decrypter. You will be able to rip the entire movie using DVDFab HD Decrypter. The only caveat for using it is that it will lag in updates compared to the commercial section, so if you are ripping new releases, it might not work on them until an update is issued.
The second tool for this that we recommend is AnyDVD HD. This has no compression capabilities...it only decrypts and rips the movie. Though there is a short trial available, AnyDVD HD has no free version. You can purchase it for a limited subscription, or for a lifetime version. It just depends on how much money you want to spend on the program. AnyDVD HD is known for being very effective, and it is updated quickly.
The third option is called MakeMKV. This program is free while in beta, but it has been in beta status for years with no signs of that ending. MakeMKV will normally take the blu ray and rip only the main movie, then put it into an mkv container file. But it also has the option to rip the entire movie to the hard drive using the Backup function. Updates to the program are fairly frequent, but will not match those of AnyDVD HD. One thing to remember about MakeMKV is that you must update the beta keys each month. They can be found here: http://www.makemkv.com/forum2/viewtopic.php?f=5&t=1053
All three of the programs can rip the movies in file format. While the trial lasts, you can rip as an ISO file in DVDFab, and AnyDVD HD gives you the option of ripping as an ISO or as files.
So now you have the movie in its entirety on the hard drive. You'll need good blank media to burn them. We recommend Panasonic and FTI made Smart Blu discs as being the best available. Verbatim are also a good choice.
The vast majority of blu ray movies will not fit onto a 25gb disc. I'd say close to 2/3rds of them that are currently available are too large for this target size. So, you should either burn to 50gb sized discs or use a program called BD Rebuilder to compress the entire movie (menus and all) to fit onto a 25gb disc. There are links in my signature down below that will take you to my guides for using BD Rebuilder. BD Rebuilder is a free program that produces excellent results.
To burn to a disc, use ImgBurn. It is the best burning program available. It is also free to download and use (be careful not to install any of the extras, like the browser add on bars). www.imgburn.com
Burn at a moderate speed. In an external drive, 4x or 6x should be fine.