Jeffrey gave you a good thought by changing to a different film for outdoor portraiture. OTOH, Tri-X is great stuff. There are (or used to be) Tri-X rated at 400 ISO or Tri-X pro (TXP rated at 320 ISO). I shoot TXP at ISO 250 and process it in either T-MAX Replenishment System developer according to the package directions. OR same ISO 250 in D-76 cut 1:1.
I avoid using polarizing filters in any portraiture. ND filters at ISO 250 probably won't help you out much. Green filters help add contrast to male portraits and require about .5 stop filter factor. Yellow is ok for enhancing blue sky making it appear darker to emphasize some nice cloud formations. Avoid using direct sunlight on your subjects. Either wait for it to soften, shoot before 10AM or after 3, or put them in a shaded area and bounce light in using a chunk of white poster board and have someone hold it for you to maneuver it around or hang it on a light stand. You should get some pleasing results that way.