Making Kombucha - problems and questions
All of your scobies look safe and healthy. They will start out thin and slimy. If you want to grow a more substantial scoby, leave your ferment for longer than usual until it is strong enough to not crumple completely and can continue to grow in future batches. 

For your food safety concerns, you want to avoid anything green, blue, or fuzzy. One method of reassurance of safety would be to keep track of the acidity of your kombucha. 

The preferable pH for Kombucha is 3.5-2.5. You can get hold of some pH strips to test this. Any pH below 4/3.5 is considered safe, amd will prevent any harmful micro organisms from growing, due to the acidity. When you first mix a new batch it will likely be above this mark, but should drop below 4 within a couple of days.