var bytes = [10,20,30,40,20,20]

int startByte = 1;
int startBit = 2
int countBit = 16;

byte[] array = new byte[]{10,20,30,40,20,20};

int size = (int) Math.ceil((startBit + countBit) / 8d);
BitSet result = getBitSet(array, startByte, startBit, countBit);

byte[] newArray= Arrays.copyOf(result.toByteArray(), size); //новый массив на основе полученных битов

 public static BitSet getBitSet(byte[] array, int fromByteIndex, int fromByteBitIndex, int bitsCount) {
        BitSet arrayBitSet = BitSet.valueOf(array);
        int fromIndex = fromByteIndex * 8 + fromByteBitIndex;
        return arrayBitSet.get(fromIndex, fromIndex + bitsCount);
    }