Just out of curiosity, which way did you try because I have a feeling it's different than what I did. Heck I'll even explain how I got it to work. While I said I wasn't sure if I should or not, after the awful day I had yesterday I'm not sure I care about anything anymore so couldn't care less what EA thinks of my post. So anyway, here you go...
Start by entering the cheats testingcheats on and cas.fulleditmode because these need to be enabled. If you aren't sure how use cheats on PS4 press L1, L2, R1 and R2 all at the same time then you enter the cheats in the text box that pops up. Next you must make sure that the sims you want to be together are all living in the same household, because you are going to be editing their relationships in CAS and I'm not sure of any other way to edit the relationships. The first marriage is pretty simple as long as neither sim is already married, just do it as you normally would. For any additional marriages between sims, go into CAS mode and set the relationship to Fiancee for the sims you want to marry. Doing this will force the two sims to be engaged, and it seems to completely ignore any additional marriages those sims may already have which allows them to be married using normal methods.
I already mentioned that the user interface doesn't seem to show the multiple marriages anywhere, but there are some other things to keep in mind. A sim can only be engaged to one person at a time, meaning that if you want multiple sims to marry one another you will need to do each marriage one at a time. I also ran into a problem where the game wouldn't let me use a wedding arch for an additional marriage, it was telling me that their fiancee wasn't around when they actually were, but I was able to click on one of the sims and do the "elope immediately" interaction. After experimenting with a household of 5 sims I noticed that after around 7 to 10 marriages the game wasn't properly registering the relationship changes in CAS, and so I had to enter CAS a second time for it to work. You will also get some pretty messed up relationships without the Player trait from the Serial Romantic aspiration, which sure you could do the aspiration for each sim but you can also use the cheat traits.equip_trait Player on each sim to add it. One final thing to keep in mind is that since the actual marriages will be done normally, you'll want to make sure the relationships are pretty high.
I hope that can actually be useful for you, and that you can get it to work.
