Just a few things spring to mind, because of my MIL 
Don't refuse to accept that sons who are old enough to marry and have children have grown up. Don't, then, continue to treat adult sons and their wives as tough they are still children. Don't commit your negative feelings, if you have any, to paper. I learned to avoid MIL after her letter to another DIL congratulating her on severing the bond between mother and son. Her crime was to marry one of MIL's adult sons. Can you see the pattern here? Even the GDCs don't want to visit.
If you want to give advice on parenting, try to remember that ideas change between one generation and the next. Advice re breast feeding, weaning etc may be very different in 20 year's time, fe, it's not set in stone.
If you have an idea of something you think DCs might like, run it by the parents before telling DCs that they can do it.
Remember that just as a DIL joins your family, so your son becomes and SIL to his wife's family, and he chose to marry her. That means he wants to live with and possibly raise children with her. That doesn't make him her possession, just as he isn't his parent's possession.
Basically, you'll be dealing with two adults who are capable of thinking for themselves and making their own decisions, raising their own children etc. and if one criticisers the other (as in DIL saying your son was out of line) have you seriously never critized your DH, ever?
FWIW I'm not keanly looking forward to my DDs getting married. My OH got off lightly, both my parents passed very soon after we got married. He did, however, get a full dose of MIL from hell first time around (I'm the second wife
)