The "b" letter sounds like "ch" in english. батьки sounds like BATCHKE... Kindly correct me if i'm wrong
The "ь" has no sound of its own, but changes the sound of the letter before it (in this case the "т"). As you say it, you widen your lips like a big smile, and let some air escape over your tongue as you release. In this case it would sound like a tiny, short "s", though it's easy to see how it could sound like a "tch" to some ears. It would be more clear with a live speaker (in person).