It is a wonderful year for Blackthorn blossom, it looks as though the trees are covered in snow in places around here. We have to hope that there is not a late frost which kills the blossom before the fruits have a chance to set.
Yes, they do have nasty long thorns which have to be avoided when you pick the sloes in the autumn. Originally the thorns were used to prick the sloes before adding them to the gin, but these days a small stainless steel spike of some sort is a better option....trust me!
Last year was generally a poor one for sloes, I wasn't able to find any within a reasonable distance of home and was glad that I had frozen some from the previous year's good crop. That was you also don't need to prick them as the freezing softens the skins for you.
Not sure what your larger tree is MrsBuffy, but probably not Blackthorn.
BTW....don't try eating the sloes when they do appear, they are incredibly bitter!