Not sure if this is the right section for this question but hoping there is someone wise here...
DH was married before and has a nearly 10 year old daughter (who we shall call A) who now lives in Australia with XW and her partner of 7/8 years. All is amicable and settled, no hard feelings on either side (as far as we know!) but we don't really have contact with them. When they moved abroad about 18 months ago, we hadn't seen A for about a year and there was no farewell meeting or anything. XW told A about her 2 new half sisters but she wasn't fussed about meeting them and doesn't really want contact with DH now (her words: "I don't know him, it'd be weird").
What I want to know is when we should tell our DDs about A. If we tell them now I'm not sure they'd understand, DD2 certainly wouldn't as she is only almost 2, DD1 is 3.5. If I leave it until they're in their teens I can imagine them being upset about not being told sooner, but where is the line? And if I do tell them, will they want to contact her? Will that annoy A and XW?
Any advice/experience, please throw it all my way, thankyouverymuch.