Androids still do not emit Ki-signals and can not be tracked by fighters trying to sense Ki. However, they do emit energy signals, which can be read by both the current generation of Scouters and the Energy Sensing of Androids. Both of these though require a close proximity to use.
Well, the twins want to be important characters in the tournament, but how and what they will do remains to be seen. I have no problem with Arcosians staying in their True Form for long periods of time, Lord Shiver will do this, though he will be referring to it as his King Form in an effort to make his race think he has four transformations. It still is quite physically exhausting, enough that when Shiver finds himself in trusted company or is in his home, he transforms down to his Diplomatic Form. However, the ability to create new forms I am going to deny, as that is supposed to be part of the mutation that made Frieza's line so powerful.
The genetic diversity of the race is not so much randomized during the larval period, as changing to different forms actually changes the DNA of each Arcosian and thus mating in different forms leads to more diversity. The one hundred population count is only counting the Purebloods, leaving roughly give or take a few, twenty-five for each mountain. The Mixed Bloods actually outnumber them entirely but are individually much weaker and considered second class citizens by the Purebloods. The cultures in the mountains do not really differ from each other, as the initial culture they had was simply to war between the clans and everything they did was focused on this. Once the other mountains were subjugated beneath the Blue clan, what few differences they may have had, such as different naming conventions were seemingly lost in time.