The two new geldings I got, have only had minimal care at best. Today I tackled the matted tails. Both of them had solid lumps from the end of tail bone down about 8 - 10 inches. It took a little over 2 hours & half a bottle of Cowboy Magic detangler, but I got it done. I really thought I was going to have to cut their tails off at the start of this. Scout's tail now drags the ground & Dakota's goes to his hocks. I wish I had gotten before & after pictures. I can't imagine how uncomfortable & painful that had to have been for them.
My friend had to do that too. At the college we went to if you didn't have a horse people around the school would send a horse that never got worked with so they could have something to do and her horse that she got had a dread lock for a tail and just like you she took 2 hours and half a bottle of cowboy magic to get it all untangled. Sadly he could only do 2 semesters before he was deemed not able to been ridden anymore because of his lack of care he developed ring bone and it was painful to do more than a walk. But he had a great year having fun and making friends with my horse. I hope you have fun with your 2 new horses and I'm sure they already love you for giving them their tails back.
Here's a picture of my friends horse and my old horse. Her's is the sorrel and mine is the black one.