As part of its programming MS Word highlights common grammatical issues such as usage of who/whom, etc. In this case, it doesn't mean necessarily that it's wrong but it points it out and relies on you to review it.
My take at this is that the more natural sounding choice would be the better one - 'is', rather than 'are'. The implication is that on that list it tells the status as to which individual (singular) is available.
As to the usage of who or whom, I might chose 'whom'. However, I'm right about 51% of the time about who or whom. Be aware that most English speakers and writers get this usage wrong 90% of the time.