It sounds as though what you want to do is extend your existing operations, rather than setting up a whole new venture.
If you set up different parts of the same commercial venture as ‘separate businesses’ purely for VAT purposes then you will be caught by what Customs calls the Disaggregation Rules, more commonly known as artificial separation.
You and your wife (or the partnership) can have separate VAT statuses for genuinely independent businesses, but it sounds as though these will be too closely linked for HMRC to see it as anything but a device to avoid registering for VAT.
There’s more information on the HMRC page: Should I be registered for VAT. If you do try to operate them separately and HMRC decide you should have registered then they can even apply registration retrospectively, leading to a hefty bill for past VAT liabilities on the internet sales.
If you want to operate separate businesses under separate VAT registrations they will need to be owned and operated independently, and demonstrably different businesses (making supplies of different things to different customers under different branding).
You’ll need to think about whether that could be realistic, and whether it would be economic – you may well make more sales using the existing brand goodwill of the partnership, enough to outweigh the inconvenience and uncertainty of attempting to operate independent trades.
And before you think about setting up the new business in Germany as another way round, that would be even less effective. From 31 October 2012, the VAT threshold for overseas businesses trading in the UK is zero – they have to register for any VATable supply at all, in line with practice in most other European countries, where you would need to register if making supplies.