Buy them, drop them in the world, and have your Sims put the items in their inventory to have them add it to their 'Household Collections.' Go to the Misc decorations, scroll through all the new items, and you'll find Sugar Skulls and the other event collectibles. In the Objects by Function menu select the Decorations tab. Enter ' bb.showhiddenobjects' and submit it. With cheats on, make sure you're in Live Mode and open the cheat box.
The Sims 4 official FAQ says that seasonal events with the NPC Jessica Holiday aren't currently planned for The Sims 4 on console, but items from past events (like Sugar Skulls, Holiday Cracker Plushies, Decorative Eggs, and Magic Beans) are still in the game.
How to Unlock Sugar Skulls and Other Seasonal Event Items You can also use this to subtract funds from your household. While motherlode and rosebud are beloved cheats, an easier way to get your sims the Simoleons they need is by typing 'Money X' with X being the amount you want to give your household.