Daughter in law problem

My daughter in law creates big,big problems splitting our family apart especially with my son.He is a smashing chap brought up to be fair in all things (he's not a saint mind you!) but close to it. When he married this lady she already had 2 children aged 8 and 12 which we readily accepted into the fold.We had no grand children of our own at that time so it was exciting to say the least. Then they had a baby which we were over the moon about, we cossetted d.i.l and baby (as much as she would allow) but felt that sometimes we were pushed out of things a little. No matter we thought, they married and thats when things began to get worse.D.I.L seems to hate the relationship with father in law and son(which is very close) and tries to start silly rows about how the kids call us by name and not granny/grandad etc. we said for them to call us what they liked and felt easiest with. D.I.L then took a stupid remark from father in law (just a silly joke) very personally and went up like a rocket with not only us but son as well.She then emotionally blackmailed us so we did not see/talk to the kids for weeks until eventually her own mother told her to forget it and move on. Things began to improve and we were happy so decided to give large amount of our money for a house extension to son and family to make a room for growing toddler. This was all going well until mother in law took cash to builder on first week and asked for his signature on a paper workbook (just for our peace of mind as it was cash). D.I.L was absolutely fine on the day but then decided the next day to not only threaten(again) to leave son and move back to her mums but that we would never see kids again. Not sure why this all happened just a day later,but she said that we were taking control?? All this emotionally charged disputing is really upsetting us very badly.We dont want them moving away as our birth grand daughter and the other kids would never see us again. This is her 3rd marriage and she has past history of upping and outing as I call it, though to be fair she was in an abusive relationship the second time round. I know what this did to her self esteem and obviously only know some parts but its like she cannot accept "good things" happening without a self destruct button being pressed. Her mother was obviously around for her (father deceased) during all this upheaval but I do NOT know what I am supposed to have done/said to start this round off, you would think that I was the evil stepmother according to her.What am I doing wrong here? She will not talk to me and explain so I am a loss what to do next. Now the building work has been soured, we can't go and see it and we don't know how to progress to resolve this situation at all.

Dear Blondie, I hope by now you have resolved this latest quarrel. I have a daughter-in-law who has two kids by previous relationship and two with my son. They are now married and two older ones grown up. I treated them the same as my own grandchildren. One thing you have to remember is to tread on eggshells here. Its very exciting having grandchildren and you want to do the very best for them, but in a large extended family things can be difficult at the best of times. You need to make a life for you and your husband that you enjoy outings etc. together regardless of family demands. They know where you are if you are needed and let them know that any help is gladly given lovingly, but recognise they are a married couple who need time for each other, which is difficult with three kids. It sounds as if your daughter in law is insecure and jealous, and probably afraid of what happened before happening again. She is obviously very sensitive as well. Just offer to have the children now and again or take them out for a few hours, to give them an evening out, etc. but if you give any financial help, better to give the money and let them deal with it. I know your son loves his parents and you probably both miss him since he is married, but his wife has to come first. I wish you all every happiness as a family. God Bless.