HMerge saved games

In each save, go to the house you built and in build mode there should be an option to save the lot to your library. Then go into CAS for each household and save them to the library as well (this should keep any skills you’ve built/kids born/pets adopted).

Finally, pick the save you want to keep, and place the other two lots from your library, overriding the default lots. Then place your households from the library into the newly built lots.

In future, when you want to create a new household in the same game, don’t go to “new” from the main menu - just load into your save and go to manage worlds and create a new household there. 

Yeah about that, there's a library for lots as in houses with all in them, so you save in build mode, then in the library you share online. Your main account save can download stuff to her/his library. You then place in build mode by clicking the library and choosing the saved house furnished. As long as the lot size is the same or bigger. Not hard to do at all, search YouTube for videos about the process if you run into trouble.

Hello Pip,
Thank you ever so much for the quick response ....sorry for the delay, but I haven't been on-line the last couple of days.
And, of course, also for the tips.....which, sort of half worked.

I first saved the houses/lots from games nr. 1, 2 & 3 to my library.
Then saved the households (Sims) from games nr. 1, 2 & 3 to my library.
This worked fine for games nr. 1 & 3...both lots and households appear in my library and I was able to transfer the house/lot  (with household) from game nr. 3 into the proper space in game nr. 1 (which is my first and main game).

However, although I keep getting messages that both house/lot and household from game nr. 2 have been saved to my library (see enclosed), neither appears in the library (although they do appear in 'News')...so they can't be transferred into game nr. 1.

I now how the situation that I can:
Open game nr. 1 and switch between the houses and households from games nr. 1 & 3 and the Sims from these two games can all interact.
Or, open game nr. 2 and switch between the houses and households from games nr. 1 & 2 and the Sims from these two games can all interact.

Strangely enough, when I make changes (i.e., plants, trees, etc.) to the outside of the house from game nr. 2....these changes are visible in game nr. 1, but when the Sims from games Nr. 1 & 3 try to interact with the Sims from game nr. 2, I get the message that these Sims (game nr. 2) don't exist. The same when in game nr. 2: I can see the changes to the house from game nr. 3...but get the message that the Sims from game nr. 3 don't exist.
Rather peculiar......
Don't know if this will ring any bells with you.....anyway, still much better having two game instead of three.
If you have any further ideas, I'm happy to listen...if not, thank you very much for the assist you have already given me.
Best,   Alex

@AlexvonAuen 

When this happens to me, it's INVARIABLY that the game has decided that the Sim in question has CC on them even when they don't, and I have to check the little checkbox that says "show items with CC as well." SUPER ANNOYING, especially in my own library! I mean, I get why they do that on the gallery, it's so people who don't want to download stuff with CC don't do it by accident, but presumably if it's in my library I own the CC!

(They NEVER have CC on them. NEVER.)

I digress. Try that and see if it works? it's a checkbox on the left.

@AlexvonAuen Your attachment looks like it's of your different save files, not your library. So just to make sure we're all looking at the same thing:

In CAS, you click the "Save Household" folder.

Then, switch into the save where you want to place the household.

Create a new household and click the "Open Gallery" light bulb.

Go to "My Library" and your saved household should be there.

If they don't show, as @xochiquetzl_xkvn suggested, try turning on CC in the left sidebar.

Open the household you want to place, and in the bottom right, click "Place Household"

(you can then delete whatever default Sim was generated when you had created the household)

As to how you somehow have some sort of link between your save files where edits in one affect another... that sounds really strange and is definitely not intended. My guess is it has something to do with the fact that two of your saves are marked as "recovered" files - are they perhaps both based off of backups / previous versions of the original save? Then it would make sense that they have some things in common - they started as one save and branched - but less sense that they could still actively affect each other.

What does your "manage households" menu look like in each save?

Dear Xochiquetzl,
Dear Pip,

Thank you both for your tips and assistance.

Both the house/lot and Sims/household in question were indeed marked as "with CC" in my library (although not true).
Have now managed to successfully move both into the first game with the other two "families".

Thank you ever so much !

Alex