hi lijaco, sorry to hear of this situation, it sounds very sad. Its much more complicated for you than for most adoptive parenst here, as its your son and his ex gf rather than just a " stranger" who is your child's birth parent.
are you thinking of setting up direct contact between you and your Dh and her? you obviously have her phone no and address and she has your number?
there is a lot to think about in terms of how needy she is, the drug misuse, the violence between her and your son, her mental health problems etc. she is also poor, homeless and has no other family support
on one hand i can understand why you feel desperately sorry for her and want to help. on the other hand, she is a MAJOR project. do you have the time, space, money and emotional energy to get involved with her?
Would you be able to set clear boundaries for your Gs and your own children's safety?
how woudl it affect your relationship with your son? she obviously wants you to get involved in their relationship eg to get him to stop sending her texts
i can understand why its hard for someone in her situation to use the letterbox system without support. But it would be a BIG decision to let her have face to face contact with your gs.