First section is my rant, second section answers your questions.
Save the money for flying, and go distance learning? Distance learning itself is expensive enough as it is, considering EASA thinks we're silly and NEED to attend x hours of ground school and get signed off by an FTO. There is really really no need to throw money at an FTO for full time courses.. Unless it's part of an integrated programme?
Also, I would avoid the UK at the moment. Not because it is a bad place (quite the opposite, did some of my training there myself) but the € to £ rate is just stupid at the moment. Especially if you just intend to sit there for 6+ months?
Unless you're made of money of course, be my guest! Just think about the 25-30K you will have to spend on a TR afterwards; Those 7 or 8k you spent on (arguably) useless classes will definitely come in handy!
As an example: my buddies and I all went distance learning and scored well (93%, 94% and one even 98%). You don't need ground school to understand the material, it is high school level at the most.. Just study on your own, and practice the databases when you're done with the books (I used aviationexam). Just set a proper study schedule and you'll be ready to sit all 14 exams in 6 months .. With time to spare to work in the meanwhile ..
Airlines know the ATPLs are just garbage .. You will not impress anyone by scoring 90+. They know you can get stupidly high marks by only preparing the question banks. They will test your in depth knowledge during the interview or through a separate paper test.
If you insist on attending ground school, have a look at Stapleford Flight Centre. They're relatively small and only do modular courses, but they have some of the best pass rates and have a few very knowledgeable instructors doing the advanced flying courses and their ground school. They also have accommodation on site, 25 meters away from the classrooms.
There is absolutely no issue with sitting the ATPL exams in a different member state. All member states have to accept each other's exam certificates. But, you will have to sit ALL ATPL exams in the same member state (all 14 in the UK, not 10 in the UK and 4 in Spain for example). Spain has to accept the UK exam accreditation. Note that because you have a Spanish license that Spain will have to issue you your CPL/MEIR as well, unless you transfer your SOLI to another member state. I would recommend sorting out the paperwork beforehand. EASA regs are great and open up a lot of possibilities for pilots and students, but everybody is still learning how it all works and thus it will take a lot longer than you would expect to sort things out.