The rector at the SSPX seminary frequently urges peacefulness during the spiritual conferences he gives to the seminarians. Peace can more or less make us invisible to the devil, and gives us an advantage over temptation which gives rise to agitation. Peace is obtained by praying for it, and by continuously exercising it in both mind and action. I have some trouble with anxiety and agitation, so I deliberately take great care to stay peaceful and careful when working to prevent a buildup of stress. It takes much effort and practice on my part to dissipate stress in stressful situations, but I have eventually become sufficiently good at it, though I may look a bit awkward. I no longer work quite as fast as I used to, so I don't get so worked up mentally. Still, there are some work related stressors that just can't be overcome.
Mental discipline goes a long way in solving many problems, and practice makes perfect. Thinking too much can cause stress and anxiety. He needs to practice shutting his thoughts off, or cutting short the beginnings of unnecessary trains of thought and paying no more attention to them. Spend much time trying to relax: listen to gentle music, learn to play an instrument, find a hobby out in nature (mine is taking pictures of very very small things; which is challenging, but exposes much more beauty in nature), spend an hour in silence staring up at the stars, go night fishing without expecting to catch anything. It is important to deliberately make silence in the mind, and though it may seem impossible, those efforts must be maintained to be successful. Just don't think, and let any sound go in one ear and out the other without any active thought. See things without paying any attention to them.
Any problems, such as success in the world (work, earning money, health, housing, ect) need to be thoroughly and confidently placed in the hands of God our father, who knows what we need and gives us good things, through Mary. Let his problems be God's problems, just seek first the kingdom of heaven. Pray for the graces to overcome these difficulties, and have the humility to ask others to pray for you, especially innocent children whose prayers, I assume, may be more favorable in God's sight.
I find taking one capsule of St. John's Wort as needed helps with peace of mind and good mood. I'll take one before fast paced hard work, so I'm not so wound up during and afterward.
Try to schedule a time to invite the priest over, so he can better guide his lifestyle. Obeying a spiritual director may reduce the chance for someone to fall into sin due to the obedience aspect. It's good to take notes too, so he can re-read the advice the priest game him. I find it most frustrating when I forget advice or forget my resolutions when I most need to remember. That's just a lack of effort on my part from not writing things down and studying them a couple times per day (where's the chest beating mea culpa smiley?).
If his duties and finances allow, maybe an Ignatian retreat or a vacation to a monastery or both would be beneficial for peace and strength of mind and soul.