both of those are rivets, sounds like you might need some new hinges.

Yes those are rivets. The hinge is called a friction stay, and if it's lacking friction (window opens too wide) then you'll need to replace

Edit: I recommend Exceed, this sort of work is their bread and butter. Often the window manufacturers don't really want this work so will quote high or be slack about calling you back.

The best option is to replace the hinges as a pair - they are rivited in, so drill out, and redo.

Ordered stuff from these guys a couple of times https://www.awsltd.co.nz/

Much thanks :)