Karmabeliever, I just wanted to respond to the 'neglect' of your DH's mother in not passing on her own mother tongue. In an ideal world, this would happen, but it's very hard to pass on a language when only one person in the family speaks it and it's not a common language (such as my DH's language). We've done the nursery rhymes and so on, but it takes a massive time commitment, and real dedication to have truly bilingual children, especially if the second language is a very minority language and not spoken in the home by the family.
I have numerous friends in mixed culture marriages who have started out with the best of intentions to teach their children their mother tongue (e.g. Danish, Dutch, French, Finnish), and successfully got them to speak a bit by the age of three, however, after that they have gone to English school, realised their mum spoke English too and unless the family has persisted and spent a lot of time and energy, the second language usually has ended up lost (i.e. the child understands a bit of it but can't actually converse themselves). I have seen it work well where English (which is highly dominant anyway) is the home language and the second language is something like Arabic, in the host culture, and one parents speaks it plus having extra Arabic classes every day. But I cannot emphasise the effort this takes to have fluent bilingual children, and to just say someone's mum didn't ensure they spoke the second language kind of implies they might not have bothered (which they might not, of course) but also risks undersestimating how hard it is to do this, and how often it fails, if my set of friends are anything to go by.