Reiterate over nested ifelse statements in R

Here is a tibble I have.

Posttest.Scenario.1.Pair	Posttest.Scenario.2.Pair	Posttest.Scenario.3.Pair	Posttest.Scenario.4.Pair	Posttest.Scenario.5.Pair	Posttest.Pair.1.Scenario	Posttest.Pair.2.Scenario	Posttest.Pair.3.Scenario	Posttest.Pair.4.Scenario	Posttest.Pair.5.Scenario
4	5	2	1	3	Driveway Drunk	Parking Lot Duo	Baby on Bridge	Homeless at Business	NASA EDP
1	4	3	2	5	Driveway Drunk	Parking Lot Duo	Down and Out	Biker Billy	Misery Mountain
4	5	3	1	2	Driveway Drunk	Domestic Disturbance	Down and Out	Biker Billy	Misery Mountain
4	3	5	1	2	Locked Out	Domestic Disturbance	Baby on Bridge	Homeless at Business	NASA EDP
4	5	2	3	1	Driveway Drunk	Domestic Disturbance	Down and Out	Biker Billy	Misery Mountain

Pardon the scenario names; they are names of police training scenarios. There are five "pairs" of scenarios. Within each pair, each participant randomly gets one scenario at pretest (already completed) and the other at posttest.

The columns named "Posttest.Scenario.x.Pair" contain the pair name (i.e., 3) in that ordinal position of presentation. For example, if Posttest.Scenario.1.Pair = 4, that means that the first posttest scenario will be the assigned scenario from pair #4.

The columns named "Posttest.Pair.x.Scenario" contain the names of the posttest scenarios allocated for each of the 5 pairs.

I am trying to create the additional five columns to the right ("Posttest.Scenario.x"). These should contain the names (rather than the pair identifier) of scenarios by their order of presentation:

Posttest.Scenario.1.Pair	Posttest.Scenario.2.Pair	Posttest.Scenario.3.Pair	Posttest.Scenario.4.Pair	Posttest.Scenario.5.Pair	Posttest.Pair.1.Scenario	Posttest.Pair.2.Scenario	Posttest.Pair.3.Scenario	Posttest.Pair.4.Scenario	Posttest.Pair.5.Scenario	Posttest.Scenario.1	Posttest.Scenario.2	Posttest.Scenario.3	Posttest.Scenario.4	Posttest.Scenario.5
4	5	2	1	3	Driveway Drunk	Parking Lot Duo	Baby on Bridge	Homeless at Business	NASA EDP	Homeless at Business	NASA EDP	Parking Lot Duo	Driveway Drunk	Baby on Bridge
1	4	3	2	5	Driveway Drunk	Parking Lot Duo	Down and Out	Biker Billy	Misery Mountain	Driveway Drunk	Biker Billy	Down and Out	Parking Lot Duo	Misery Mountain
4	5	3	1	2	Driveway Drunk	Domestic Disturbance	Down and Out	Biker Billy	Misery Mountain	Biker Billy	Misery Mountain	Down and Out	Driveway Drunk	Domestic Disturbance
4	3	5	1	2	Locked Out	Domestic Disturbance	Baby on Bridge	Homeless at Business	NASA EDP	Homeless at Business	Baby on Bridge	NASA EDP	Locked Out	Domestic Disturbance
4	5	2	3	1	Driveway Drunk	Domestic Disturbance	Down and Out	Biker Billy	Misery Mountain	Biker Billy	Misery Mountain	Domestic Disturbance	Down and Out	Driveway Drunk

Here is what I wrote, which gets the job done:

  rowwise() %>%
  mutate(`Posttest Scenario 1` = ifelse(Posttest.Scenario.1.Pair == 1, Posttest.Pair.1.Scenario,
                                 ifelse(Posttest.Scenario.1.Pair == 2, Posttest.Pair.2.Scenario,
                                 ifelse(Posttest.Scenario.1.Pair == 3, Posttest.Pair.3.Scenario,
                                 ifelse(Posttest.Scenario.1.Pair == 4, Posttest.Pair.4.Scenario,
                                 ifelse(Posttest.Scenario.1.Pair == 5, Posttest.Pair.5.Scenario,"NA"))))),
         `Posttest Scenario 2` = ifelse(Posttest.Scenario.2.Pair == 1, Posttest.Pair.1.Scenario,
                                 ifelse(Posttest.Scenario.2.Pair == 2, Posttest.Pair.2.Scenario,
                                 ifelse(Posttest.Scenario.2.Pair == 3, Posttest.Pair.3.Scenario,
                                 ifelse(Posttest.Scenario.2.Pair == 4, Posttest.Pair.4.Scenario,
                                 ifelse(Posttest.Scenario.2.Pair == 5, Posttest.Pair.5.Scenario,"NA"))))),
         `Posttest Scenario 3` = ifelse(Posttest.Scenario.3.Pair == 1, Posttest.Pair.1.Scenario,
                                 ifelse(Posttest.Scenario.3.Pair == 2, Posttest.Pair.2.Scenario,
                                 ifelse(Posttest.Scenario.3.Pair == 3, Posttest.Pair.3.Scenario,
                                 ifelse(Posttest.Scenario.3.Pair == 4, Posttest.Pair.4.Scenario,
                                 ifelse(Posttest.Scenario.3.Pair == 5, Posttest.Pair.5.Scenario,"NA"))))),
         `Posttest Scenario 4` = ifelse(Posttest.Scenario.4.Pair == 1, Posttest.Pair.1.Scenario,
                                 ifelse(Posttest.Scenario.4.Pair == 2, Posttest.Pair.2.Scenario,
                                 ifelse(Posttest.Scenario.4.Pair == 3, Posttest.Pair.3.Scenario,
                                 ifelse(Posttest.Scenario.4.Pair == 4, Posttest.Pair.4.Scenario,
                                 ifelse(Posttest.Scenario.4.Pair == 5, Posttest.Pair.5.Scenario,"NA"))))),
         `Posttest Scenario 5` = ifelse(Posttest.Scenario.5.Pair == 1, Posttest.Pair.1.Scenario,
                                 ifelse(Posttest.Scenario.5.Pair == 2, Posttest.Pair.2.Scenario,
                                 ifelse(Posttest.Scenario.5.Pair == 3, Posttest.Pair.3.Scenario,
                                 ifelse(Posttest.Scenario.5.Pair == 4, Posttest.Pair.4.Scenario,
                                 ifelse(Posttest.Scenario.5.Pair == 5, Posttest.Pair.5.Scenario,"NA"))))))

But I know that's horrible and couple be vastly improved. I just don't know how to do it. Is it a loop that uses a function? Can you please help?