We are relatively new to Platinum and usually travel alone, but this summer we will have friends accompanying us to Spain. Will we be able to have them join us in the Concierge lounge?

You should be okay. Most hotels will extend concierge lounge access to rooms if the other guests are traveling with a gold/platinum member.

How many friends are coming with you, and how many rooms are you paying for? If you had only one gold/platinum room and 10+ rooms of non-elite friends, you could run into trouble.

We have one room and they have one room (they are silver)

No ser� un problema.

I did this at two different properties in the past week and there was no problem.

In fact, both rooms were reserved under my name at both hotels. When we checked in, each rooms' keys were coded for CL access, despite my friends having the reservation switched to their names, info and credit card at check-in.

This worked out well, as the other room's occupants could have CL access without having to have a copy of my room key ..., umm, rrrr, ... I mean without my having to be there. (Please do not infer this as a suggestion that you give your traveling companions a copy of your room key so they can access the CL at anytime. I'd never suggest this simple solution. Especially if they have a sixteen year-old who uses his key to get snookered in a European hotel for free, although it's doubtful anyone would be lame enough to do that. Again. )

the only places that you may have any issues are those that are staffed with a desk person checking your name to a list

they may/may not ask how many guests? some (not the majority) may try to charge you a fee