Hello Dragonfly. Thx for the Thx. In regards to employer or union subsidized lawyers, he will have to talk with co-workers to get an idea about how good or bad they are. Unfortunately some are great and some not so much.
Peace has given you good advice about staying away if you think you may say something.
In regards to the courts being fair. I agree that they are sometimes very unfair, but courts have this modern view that for better or for worse are merely words. They tend to take the view that people are liable to grow apart for various reasons and that blame should not be attached when this occurs. I'm not saying that this should always be true, but it is a modern reality whether I like it or not.
In regards to costs. When your son talks to a lawyer, the first thing that he should ask about are the fees for an uncontested divorce. If it gets contested the costs will be huge. The biggest unexpected costs that comes as a shock for most people is if the ex spouse gets sole custody of the children. You can find out details at
http://www.justice.gc.ca/eng/fl-df/child-enfant/fcsg-lfpae/2011/index.html and then scrolling down to Ontario, 1-4 children. If a person makes around 70,000 a yr and has 3 kids, they can expect to pay 1356 per mth. This causes a lot of people to pause and decide whether or not to go for sole custody and hire a nanny.
In a shared custody case, you take the ones person income minus the other persons income to figure out the net income. Say your son made 70,000 and his ex 20,000 the difference is 50,000 and the tables can be used to figure out the amount of support, about 1000 in this example. Those are just examples. The judge can award more or in rare cases, less.
If your son has family benefits through his workplace for his ex-spouse and his children, tell him not to cancel them until he speaks with his lawyer. I know he won't for the kids, but some guys like to cut their ex off of the benefits only to find that they are sometimes responsible for her benefits too.
A fairly good resource that explains the terms better than I do and explains the laws fairly clearly is
http://www.canadiandivorcelaws.com/spousal-support/ , just click on the various categories at the top of the page. They also have a section on alimony.
Also warn him about signing any separation agreement before seeking a lawyers advice. Some parts of a separation may seem like a good deal, but when all the legalities are figured in they can cost more than a person thinks.
One final word(s), and again no judgement is intended. Parents love their kids. We ,or at least, I , tend to think that the other person is 100% at fault, when a marriage or relationship goes sour or has problems So while I'm sure that you are quite upset with the whole situation, I'm sure that your daughter-laws, mother is going to take her daughters side. Rightly or wrongly.
I can't speak for anyone else, but sometimes I have to remember that my own Mother-in-law(who is a really nice person) is going to nearly always side with my wife(which makes me mad at times) My wife is a great person, but she does have flaws that sometimes can drive me a little crazy (very short drive LOL) . When my kids have problems, I have to be very careful that I don't see just their side of things as well. So while you can think harsh thoughts about your daughter-in-law, please remember that no matter what she has done,her mother is going to still love her and by default side with her in any major decisions. It's the way nature created us. Other wise we would never have kid because at some point in our lives our kids are probably going to cause us many sleepless nights. I did for my parents and now my kids are repaying me LOL.
While I hope that this gets settled quickly and to everyone's satisfaction, I'm sure that you will need all the support you can get. So post here freely. From now on I will try, I repeat try

, to keep my answers a little shorter.Good Luck and Take Care. paul m.