Interplay of neuritic and synaptic growth
Short answer
Both short and long-distance synapse formation can occur.  

Background
Short-distance connections can be made between adjacent cells (Van den Pol et al, 1988). Your 'common ancestor part' is a bit obscure to me. In the end, every cell is born out of a single one :)

Long-distance connections can also be made. For example after neuroneogenesis either during development or even in the adult brain, whole neurons can migrate from their origin to a new part (Kaneko et al., 2017), or axons can grow to find a new target distally, for example after neural injury (Purves et al., 2001).  

References
- Kaneko et al., J Neurochem (2017); 141(6): 835-47
- Purves et al. (eds), Neuroscience (2001), 2nd ed. Sunderland (MA): Sinauer Associates
- Van den Pol et al., J Comp Neurol (1998); 399(4): 541-60