Why are some of my pictures smaller than others?

Hi,

I am pulling my hair over this, I am sure I have done something silly / stupid, but it was all working ok, but now every picture I post is too small.

https://siciliandream.wordpress.com/2014/12/15/the-journey-begins/

It is very obvious here, on this page,

The first two pictures look much smaller than the last one despite being the same physical (and as far as I can tell) memory size.

The last (3rd) one is perfect, all I want to know, is how do I make the other two (which I added later) match?

Thank you all for any help you can give.

It will be really appreciated

Lyn