Run, run for your life. No, I'm just kidding. I am the loving parent of two grown daughters and we had a ball when they were growing up.
Parents of multiple children need to be sure that each child has a moment or a special time with each parent...a real chance to have their time and attention.
Let me share a very unpopular notion. Sharing is over rated. When two children are asked to share, the dominant child is the one who gets the toy (or whatever). Observe kids carefully in preschool, or even your own kids. One child, usually the oldest will be stronger and stronger willed. That child will be the one who gets the most time with an item that is supposed to be shared, leaving the other child wanting but unable to act.
I think providing children with their own toys etc. teaches them pride of ownership and learning how to care for what belongs to them. That is not to say kids cannot, or should not be taught to share - but it needs to be implemented carefully and with supervision to be sure things are fair. Many things like taking turns are learned and become habits. The parent needs to supervise, letting each child know that their turn will come - and making sure that it does. My grandkids learned this quickly and do it beautifully now. Of course there is always the battle over who goes first! :-)
Sibling conflict - holy moley, if you can find a cure for that, please do publish a hub about it. I dealt with it on an event by event basis. I taught our girls that I would always listen to each side. The other one was not allowed to interrupt while I was listening to one side and if they did I told them, Wait, your turn, I will listen to every word when your turn comes. It worked pretty well.
But of course they fought - she's touching me!!! She looked at me!! I think that is just human nature and they are great friends now.