On the accent/dialect/'style' issue: I suggest you folks do some research...
1) Kids just need to practice and gain confidence/usage, it doesn't matter if the NS is from England, US, Ireland, Convictland, etc - language is language; the differences between dialects are tiny compared to the similarities. For the kids to have a few different types of NS is ideal.
2) The language is not converging, and we will not all be speaking English English or American English in 50 years... Look at the UK and the massive quantity of dialects, we have not converged despite the political efforts of the elites around London. The same is true in the US; one landform, hundreds of years together, but the language is still evolving and changing in different directions - welcome to planet Earth; and we're all the better for it...
Cultures and societies mix together in many different ways, to name but a few: Microsoft, Apple, etc, push American English spelling; BBC, CNN and most international news organizations generally use RP English; Thais use Tinglish; MOST non-native speaker usage of English is with other NNS, so it's just as likely as K-pop, J-fashion and Chinese growing business practices will push their culture into English; the list goes on and is always reinventing itself. This British English v American English is imperialistic nonsense...