You don't say what ages they are...that makes a big difference.If they are both under 10, you can quickly now tell them your ideas.
In other words 'how' you feel they should respect each other.Also you can try to be the one in between them, so no fights happen.A gentle hand, to guide them along.Encourage them, and have a reward system.
If they are between 10-15, you can do the same....but you need to use a lot of wisdom, so they do not know your watching too often, but! you are aware of their issues.You also have the Adult card to pull-out too.''Your the parent, they the child''....but you use it only on certain issues.
If they are over 15, you may have waited a tad too long....but you can still be there, just not as much of a heavy hand.Only if things get really out-of-hand do you pull the ''Adult Card'', and it is your right to do so.
Well then you can make it happen...that they grow up respecting each other very much.That's what it really is about.My two eldest sons were 18 months apart, and I insisted 35 years ago....they treat each other with love.
Only when they were grown men, working together did they have issues, in our family Locksmithing business...which is expected, really.
Sibling rivalry is going to happen no matter what; in most case it will just be healthy competitiveness or the slight bit of jealousy. It tends to get more serious if there are major gaps between ability or if one seems to get more attention than the other. Treat them both equally, but as separate individuals. Give them group attention so you can all bond together, but also give of them your own individual time so they don't feel like they always have to share affection.
Sibling rivalry is super annoying for the parent - but sometimes I notice that it creeps in when the kids don't have enough to keep them occupied - so they create a game, and sometimes an argument is a game (albeit not a very fun one). My tip is to keep the kids occupied.
As the youngest of four I thought it was good that my parents didn't compare us. Like 'she got top marks why didn't you or your sister would never do that'. All of us were and still are very different with different personalities, interests and skills and my parents have always respected that and thought it just made us all the more special, unique and just used to laugh about it.
Sibling rivalry in my view is a behaviour that reveals deep seated worries around acceptance, self worth, the future and being recognised and valued. What it takes is conscious actions by the parent to ensure they do not exacerbate these issues, and go out of their way to overtly be equal to get to a place where the jealous child is able to identify and manage their own feeling without it being conflated by other external forces. I have lived through this and it can be mitigated through careful parenting and support of both the child or who feels jealous and the one to whom the jealousy is being directed.