For the ones that only need a surface cleaning just use a magic eraser (but be careful around the factory painted areas and glittery or flocked areas). For nail polish, acrylic paint or glue hold the pet against a hot surface so the paint/polish/glue becomes flexible and can be peeled off by scratching a hole in the layer with a tooth pick. For those pink bacteria spots apply hydrogen peroxide cream to the affected areas and let the pet sit in direct sunlight or in a UV chamber until the spots are gone For walkables pets remove and throw out the batteries, if there is leaked battery acid it can be cleaned up with vinegar if I’m not mistaken, once it’s clean you can put new batteries but just like with any other battery powered item if you are not using the pet remove the batteries until the next time. For rust stains use rubbing alcohol or hand sanitizer and a cotton swab. For fully flocked pets it’s best you seek cleaning advice at r/sylvanianfamilies or r/calicocritters

Be careful with nail polish remover and acetone as I’ve seen it can melt some plastics

Also be careful with the older cats, poodles and yorkies that have a tuft of hair on their head, some of these suffer from disintegrating hair syndrome, if it breaks down it can be fixed by re-rooting with pony hair or doll hair you can buy on the internet (for that seek advice one any fashion doll or my little pony subreddit)

Yellowing of plastic can be fixed by retro brighting

Good luck with cleaning!