I have zero experience with EUFI, so, I can't help you...
But, surely... As always, there must other people on the Internet explaining how can one manage Windows and GNU/Linux partitions with UEFI. (Look for that information, using a search engine.) And, it seems like an easy problem to solve.
Trisquel is based on Ubuntu - which has an immense number of users. And, you can find a lot of responses for Trisquel problems if you search on the Internet for the same problem in the Ubuntu version that your Trisquel version is based on.
Trisquel, or GNU/Linux, in general, in this particular case - since, this is a generic GNU/Linux problem - is not as "simple" to use as Windows. So, you'll have to be more patient for any problems that may arise, and prepare yourself to spend a good amount of hours learning how to use it, before you can operate with it well.
If you're not willing to do that, then it's your choice... But, I think it's worth the time and patience invested, because of all the /real/ security, and other things, that you can only get with GNU/Linux.
I also had the same type of frustrations, at start, and would say the same type of things, that you're saying... But, having found the patience to solve the problems that would appear, I am now immensely glad that I did it... Since, there's nothing better - and, above all, more secure - than this OS... And, after some months using it, I, long ago, decided to never go back to Windows again.
