Can an indoor primer be used to prime bear wood weather boards?

We are painting our 3rd floor condo which we plan to sell shortly. It is completely painted but we have a common wall with the foyer of the condo and it has a lumpy texture to it. We think perhaps this is affecting our wall that butts up to it.

The garage doors are rubbed down and washed with sugar soap. Can I do a coat of emulsion paint or do I need to go and buy undercoater?

I have just had my walls plastered and my decorator has primed the walls. But now I have brown spots coming through. I have tried the sprays and they are still coming through. Can you help?

What do you call missed spots after painting? What is the slang word?