Dear FIL and MIL,
Have you ever noticed that you have better relationships with your friends than you do with any of your family members?!? Im not sure how your friends are actually friends with you, except that you treat them completely differently.
If this is the case than I highly recommend you consider treating your family members like you do your friends.
The reason we never call you or visit you is because we only get in trouble for doing SOMETHING whenever we see you (and for that matter when we don't). Its not enjoyable for us to make arrangements on one of the 2 nights we have together just to be miserable and get in trouble for whatever the issue of the day is.
You want us to have a great relationship with you, but we refuse to put up with your BS, so either you can straighten up and treat us nicely, or you can risk losing another familial relationship, which would leave you with what - 2 familial relationships?
P.S. Sending nasty emails to "reintroduce" yourself to your son is immature, rude and completely unnecessary (kinda like this post - except this at least will provide stress-relief for me, entertainment for others and theoretically, you'll never see it).