ifelse with sorted values by row

I have a dataframe (example data):

id <- c(1, 2, 3)
ex1 <- c(0.8,   0.2, 0.3)
ex2 <- c(0.1,   0.4, 0.04)
ex3 <- c(0.04,  0.3, 0.5)
ex <- c(1, 1, 1)
ran <- c(0.5, 0.7, 0.6)
dat <- data.frame(id, ex1, ex2, ex3, ex, ran)

dat
  id ex1  ex2  ex3 ex ran
1  1 0.8 0.10 0.04  1 0.5
2  2 0.2 0.40 0.30  1 0.7
3  3 0.3 0.04 0.50  1 0.6

I want to changes the values of "ex" with an if-else-condition. "ex" should change to 5 (arbitrary) when "ran" is smaller or equal then the highest value for the ex$-variables. It should be greater then the other ex$-variables aswell, but they should be sorted - the second largest value added to the smallest value. Here are examples for all id's, beginning with id 1:

dat$ex <- ifelse(dat$ran <= dat$ex1 & dat$ran > dat$ex1 + dat$ex2, 5, dat$ex)

Here, ex1 is the largest value, followed by ex1 and ex2.

For id 2, it should be:

dat$ex <- ifelse(dat$ran <= dat$ex2 & dat$ran > dat$ex3 + dat$ex1, 5, dat$ex)

Here, ex2 is the largest value, followed by ex3 and then ex1.

For id 3:

dat$ex <- ifelse(dat$ran <= dat$ex3 & dat$ran > dat$ex1 + dat$ex2, 5, dat$ex)

Here, ex3 is the largest value, followed by ex1 and then ex2.

Now to the problem: How to generalize the ifelse-statement? Note: It is important that the summation of the two smaller values is performed as implemented in the examples. I need to identify the sorted values for ex1, ex2 and ex3 within ifelse by id.