(1) He is married to Geesien Harmannus Bok.
They got married on August 4, 1808 at Oude Pekela, Groningen, Nederland.Source 4
Child(ren):
(2) He is married to Trientje ten Heuvel.
They got married on July 8, 1791 at Obdam, Koggenland, Noord-Holland, Nederland.Source 5
Child(ren):
Married before with Trijntje ten Heuvel, who had a child called Aaltje Adams (1792) that married in 1816 in Nieuwe Pekela, while Trijntje was born in Medemblik: http://www.allegroningers.nl/personen/weergave/akte/layout/default/id/bf0080c0-87b7-30c6-f6a4-720f55dd5e30/q/persoon_achternaam_t_0/adam*/q/persoon_voornaam_t_0/harman*/q/persoon_rol_s_0/0/q/persoon_rol_s_1/0
In 1796 they also had a daughter called Mietje Adams in Medemblik, marrried in Nieuwe Pekela. https://www.wiewaswie.nl/nl/detail/6620202
In 1793 they had a daughter called Frederika Adams, Medemblik married in Nieuwe Pekela https://www.wiewaswie.nl/nl/detail/13911755
However, there's quite a distance between Medemblik and Oude Pekela, although he is 10 years older than his wife, they married late, so he could have had a previous relationship, and the fact that his children get married in Nieuwe Pekela while being born in Medemblik makes it enough for me to conclude.
In the death certificate it says he leaves behind, of a previous marriage, 3 children and of the current marriage 4. This is also correct with my assumptions.
Frederika's marriage certficate notes that her mother died in Oude Pekela.
Johannes Harmannus Adams | ||||||||||||||||||||||||||||||||||||||
(1) 1808 | ||||||||||||||||||||||||||||||||||||||
Geesien Harmannus Bok | ||||||||||||||||||||||||||||||||||||||
(2) 1791 | ||||||||||||||||||||||||||||||||||||||
Trientje ten Heuvel |