The Utrecht Archives contains many online resources. In particular is the database of extracts and digitised images of certificates of notaries who resided in the city Utrecht. The database contains over 167,500 extracts for the period 1663-1783, all having digitised images.
As Utrecht was the base of much commerce with the Demerara colony, many contracts are contained in this archive relating to families in Utrecht with connections to Demerara. Searching for ‘Demerarij’ and variants results in 62 hits covering the period 13-10-1750 to 15-03-1809. I wish my Nederlands was sufficient to let me make more sense of these. For me, the most significant of these is the the document that links Hendrik Van Cooten of Demerara with his family in Doorn. I have put up a transcript and translation of this document.