No direct advice other than the relatively obvious - contact the companies involved before you default on payments and explain the circumstances and ask them what they can do to help you, and more importantly ask them what obligations they expect you to maintain. This will generally save you trouble and make life much easier than having them send you Mahnungs.
From the other angle see if there's a '
citizens' advice' like organisation who can explain you your rights and detail what the companies can force you to pay, what they are likely to persue you for, and what they'll most likely let drop. IIRC someone posted some information about the German equivalent but I have no idea what it's called.