This is what I found in my legal dictionary. It may help you a little. The sentence means that although the person answering the question does not actually (factually) KNOW for certain, he/she disputes that the Antragsgegner is married and has two other (further) children. Sort of saying, it does not seem likely although I do not know for sure.

Romain: mit Nichtwissen bestreiten = to raise the plea of lack of knowledge. It's hard to tell how to handle the German passive voice here.

The respondent/petitioner pleads lack of knowledge as to whether the respondent is married in Ireland and has two more children.



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Note added at 26 mins (2006-11-21 05:27:18 GMT)
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Pleading lack of knowledge.
“The allegations of paragraph [n] are denied for lack of knowledge or sufficient information to justify a belief therein” is bad writing. Yet many of us who would never write like that in briefs frequently do so in pleadings. Rule 8(b) requires the pleader who lacks knowledge to say so, and that has the effect of a denial. To obey Rule 8(b), plead lack of knowledge like this:
Schmidlap lacks knowledge or information sufficient to form a belief whether paragraphs 8, 9, and 10 of the complaint are true.

http://raymondpward.typepad.com/newlegalwriter/2006/01/simpl...

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Note added at 4 Stunden (2006-11-21 09:51:12 GMT)
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Der Antragsgegner bestreitet einfach, dass er verheiratet ist und zwei Kinder hat.