1) '"i.W." may be an abbreviation of "in Wertung," making the whole phrase mean "valued at 25,000 euros."
2) "hiervon" can mean "of it" or "of that" or "of them." The whole phrase may mean "controlling interest in business shares or partial business shares."
3) "Stammeinlagen" may mean "initial investments," and the whole phrase may mean "insofar as this concerns the ban on repayment of initial investments."
I feel very diffident and tentative about these interpretations, and would like to know the wider context.