Part 1 is here (not important to solving this one)
My prefix is an H bent outwards minus end three;
My infix weighs fourteen pounds, minus the letters in me;
My suffix is an uncle's brother's grandsons, minus the first one;
All together, I'm in machines, but don't get me stuck to you when you're done.
P.S. (not really a hint but still)
You can assume the uncle in question has only one brother.