Me, DP my dd7, ds4 and his ds7 are coming together as a blended family. DP is in the process of clearing out the last of his stuff from his house and by next weekend we will be officially living together. All is mostly positive, dd and dss are really close and play together lots while ds tags along after them. They all seem very happy.
But one teething problem we are struggling to find a solution to is that dss has his Wii over here with his many Skylanders. They have been enjoying playing with these together Only now dss has expressed he doesn't want my dd playing with them when he's not there when we've already let them play with them. I can totally understand dss's sentiments but equally it's hard to have them about the house and say that my kids can't play with them. We are thinking that we could get my dd some of her own Skylanders but we're not made of money. Or ask dss to say which she can play with and which he wants to keep aside. We need to find a compromise somehow.
I think it's an issue that arises in non-blended families. One sibling will want a special toy to be theirs, and be able to give/withhold permission to a brother or sister. (If you've just had one child till the 'blending' started, you won't have had to deal with it.)
But those who have more than one child will be used to cries of, 'But it's mine'. 'He/she went and played with it without asking. It's not fair.'
So I suppose your child is finding out something about (step)siblinghood.
We had similar issues when we moved in together. It is particularly an issue in blended families because the DCs need to get used to their parent and home being used by some other children when they're not around, and still feeling at home there when they are. So important that they feel they have some control over their own things.
The compromise we came up with was that all DCs could keep any games that were special to them in their rooms, and others could not play with these without prior permission. They do this particularly with games that have save points on them, where someone else playing on it whilst you're not there spoils the game for you. Any games that are left in the living room are fair game to be played by all. This encourages tidiness too If your DSS is sharing a room, then make sure he has some private space within it, preferably out of sight (eg some drawers) that he can keep things like his favourite game in.
But you probably do want to get your DD at least one Wii game that she really enjoys for her to play when DSS is not around.
In fact it really hasn't been much of a problem at any time - the DCs make their own arrangements over borrowing stuff when the other lot are not around and they seem - mostly at least - to find solutions that they're all happy with.
We have a blended family of primary aged children and often have the same "sharing" issues.
We usually do it on a case by case basis and either myself or DP will make the decision as to if something should be shared or not.
Skylanders in particular, as all the children have ones that have been bought for them. However, they do not get "used up" they are unlikely to get broken as just lifted up and placed down, so we have told the children they must share these. Although they all have their own account on the game so each child's save game is separate meaning the fun isn't spoilt if one of the others plays with it when they are not there.
We do not make them share special items, of things that can only be used a limited number of times etc. We are also careful to only enforce toy sharing where age appropriate, so the younger ones are often told they can't play with the older ones toys.
Things like books, garden toys etc are all fair game here, so anyone can play with them. Seems silly to have toys sat not being used when another child could be (carefully) enjoying them. However, if they were to e disrespectful and or brake one anothers toys then I guess it would be a whole different story.
The rule in our house is that all wii games (and skylanders) belong to all of them. This is because when we got together they had a lot of duplicates so we traded them in and they got new games with the money. They each have a DS and have their own games for those and they tend to sort these out amongst themselves but the only thing they are territorial about is the Lego! If anyone breaks up another's Lego spaceship or whatever there is hell to pay!!! DSD is the lucky one - nobody wants to play with her Monster High dolls and her 'pink cupboard' is all her own!