I have no real experience with RootsMagic. Maybe someone else on this forum can give you a better answer.
The usual route is to create a new PAF file and then import the gedcom file. I use PAF gedcoms all the time that have multimedia links, without any trouble. Does RootsMagic allow you to chose an export format that is more specific than GEDCOM 5.5? This might solve the problem.
Custom events can be a problem if they don't conform exactly the gedcom spec 5.5. But maybe these are items your relatives can live without. PAF normally tells me what items are missing from the spec.
PAF allows only one principal name per person. It also allows: Also Known As, Nickname, and Married Name as three additional names. Look at the RINs of the individuals to see what is causing the problem. PAF 5 puts the surname between slashes, as in Henry /Smith/ or /Lau/ Mei Ling. An error may be the presence of one slash or three slashes, which the program is unable to interpret.