just take the yoghurt out from the fridge 15 mins before serving. I made all fruit puree by myself. I'm not sure how old your bb is, apple and pears are the best fruits for young babies (6-7m), after that you can introduce papaya and peach.
For the avocado, just cut it in half, and use the spoon to soft it up until smooth
Sweet potatoes, it's okay for both yellow and purple one I guess. I bought the organic one, so it usually comes in yellow. Just steam them and blend it up, add milk to turn it into the right texture
Banana/ papaya / mango puree - just use a fork to mash them
apple/pear/peach puree - if your bb is older than 8m, you can use a spoon to do it. But I prefer to steam it, becuase my bb is still young, and fruits will not change to dark after steam
For yoghurt, she can only take 1/2 cup every time, so, she will have 2 days in yoghurt and might be bb cereal the next day, and avocado for two days (as she can only take half each time)