Only in Spain do they use "os" for second-person-plural indirect objects (IO):
- Os ofrecemos un descuento. ("os" is the IO, while "un descuento" is the direct object.)
"os" can also be used as the direct object (DO):
- Os invitamos a participar.
In all other variants of Spanish, instead of "vosotros" the form "ustedes" is used, which is conjugated just like the third person plural "ellos". Therefore, "les" is used for IO and "los" or "las", depending on the gender, for DO:
- Les ofrecemos un descuento. (which, according to the context, can be interpreted as "We offer you(plural)/them a discount.")
- Los/Las invitamos a participar. (which, according to the context, can be interpreted as "We invite you(plural)/them to take part.")