I have been a long time believer that most of intonation problems are associated with tone. If the players in your quintet were to work on matching tone quality - most of the intonation problems might go away.
Quintet is a 'tell-all' setting. Each player is a soloist, and cannot hide behind another part or player - which gives emphasis to the tone problem. If one player is using equipment or a physical set-up that causes the pitch to be especially bright (more high overtones) one might mistake this for 'sharp' then try to adjust... which only produces more intonation problems, makes you tired, and wears heavily on the ears.
Here is a suggestion - record if possible
#1 - have the tuba play the root (like Bb or something) with a tuner
#2 - after it locks in have the trombone play the upper octave
#3 - Horn adds the third
#4 - 2nd trumpet adds the fifth
#5 - 1st trumpet add the octave
Play these chords at a reasonable volume level
#6 - upon appropriate que, move up one half step (return to the original
chord, move down and return to the original chord and hold it)
#7 - using the same formula, up a M2, m3, M3 and etc.
What this does: gets you to listen, and find the nature of the problem. The only way to fix a problem is to find it - and then experiment with solutions. Its also a good warm up for a group. Gets you moving together and adds the tuning factor.