I know this has been discussed before, but I can't find it in search and my circumstances might be slightly different.

Flying to northern Latin America next week with two non-status friends. I figure for my domestic leg I will give my upgraded boarding pass to one of my friends, and it probably won't be a problem (very full flight, no need to fuss with telling the FA).

For the intl portion, the load is light. Will the FA notice? Will they care? Should I tell them? Do they check passports at gate when boarding?

Thanks.