Whena child, of either sex, partners up seriously, whether married or anything else. The parents immediately cease to be the most important person in that persons life.
As the bible says: For this reason a man shall leave his father and his mother and be joined to his wife, and the two shall become one flesh. This applies to all serious relationships.
You should not really have dropped in when they first married, unless you had first asked whether you could and given them a call in advance, but that is an easy mistake to make. But your later actions really suggest that you are completely emotionally cloth-eared.
Your DS and DDiL are an entirely seperate household made up of two people who grew up in different families and now they are married they will be building up their own family dynamic, some of their upbringings will be accepted, others ignored and they will introduce their own personal preferences.
Your son is handling this difficult situation as well as is possible.
As others have said, flowers and a nice card could help to redeem the situation and then whenever you wish to visit especially when they do succeed in having a baby, remember the parents will dictate how and when they want you to visit, always ask and always be complacent no matter what, and offer no childcare tips unless asked. Childcare has changed immeasurably since you or I were first time mothers.
I had a friend with a mother like you. in the end she and her family moved 20 miles away, somewhere difficult to reach by public transport (her mother did not drive) in order to reduce the number of times she just dropped by - and offered loads of 'helpful' advice on bringing their children up.