Possibly ill birds?

Over the last 2 days, two birds (which we think may be young collared doves) have landed in our garden and not left. They don't appear to have any obvious injuries, and they are both able to fly as they keep moving to different parts of the garden. It seems strange to us that they have not left and we are worried they may be unwell, but we're unsure how to tell! They also seem to stay very close to each other, if they aren't sitting right next to each other they stay within reach of the other. I've attached some pictures below - thanks in advance for any advice!