She could seek some legal advice. If the contact has been consistent and positive and her son is enjoying his visits then she could apply for an increase in contact. The courts would be looking at what is in the child's best interests. Family courts are now making orders for separated parents to attend courses where they try to come to a joint agreement about what is best for their child - they attend different groups. If they cannot agree then the court will rule.
If your grandson has half siblings then the court will take into account the need for sibling contact as well.
Your daughter may be entitled to legal aid, ring your local woman's aid and ask if they can recommend a solicitor in your area who specialise in childcare work.
Many estranged parents i know have fortnightly contact and share the holidays, birthdays, Christmas etc. CAFCASS have a website and may have recommended books for children whose parents have a poor relationship.
Going down the legal route may result in better contact but you need to weigh up how the whole process will effect your grandson, would his birth father put pressure on him to say he did not want to go. Every situation is different but if everyone loves the child and focusses on what is best for him then a good outcome can be achieved .
Good Luck
NEVER EVER HAVE I - Game 2 (Alphabetical)
What do you think would go well with coasters like this?
To go through chemo therapy or choose not to?