Oz would have been at Hogwarts by the time she joined the nursery and already Far Too Important to deal with "kid stuff" so I don't think he'd have much of an opinion on her prior to her being Lowri's maid. He wouldn't be mean or unkind just not that involved.

Don Juan on the other hand is of an age with her and would have treated her like another sister, for better (being protective if she ran into trouble at Hogwarts) or for worse (pulling her hair when they were kids). He would have been especially fond if she indulged him in his antics (eg, let him be the dramatic hero when they played make believe, did not point out the immediate logical flaws with his various passing fancies). Has probably leaned on their shared childhood at least a few times in adulthood to try and get her not to tell his mother things. If she did anyway, he'd call her a traitor and act like he was mad at her... then forget about it while he goes off on benders for a week or more and probably leave her fretting about how he's determined never to speak to her again.