Adpositional marking with fi + possessor is not restricted to topicalized contexts, although some speakers use the construction only in them. Those speakers who use the construction even when the focus particle da does not occur in the sentence say it is more emphatic than the construction with a preposed possessive only.
In the 3rd person plural, some speakers perceive dehn to express collectivity as opposed to dem (individuality).
Source: Bartens 2003: 52
Source: Bartens 2003: 52
Source: Bartens 2003: 51