The formation of massive planetary or brown dwarf companions at large projected separations from their host star is not yet well understood .
In order to put constraints on formation scenarios we search for signatures in the orbit dynamics of the systems .
We are specifically interested in the eccentricities and inclinations since those parameters might tell us about the dynamic history of the systems and where to look for additional low-mass sub-stellar companions .
For this purpose we utilized VLT/NACO to take several well calibrated high resolution images of 6 target systems and analyze them together with available literature data points of those systems as well as Hubble Space Telescope archival data .
We used a statistical Least-Squares Monte-Carlo approach to constrain the orbit elements of all systems that showed significant differential motion of the primary star and companion . We show for the first time that the GQ Lup system shows significant change in both separation and position angle .
Our analysis yields best fitting orbits for this system , which are eccentric ( e between 0.21 and 0.69 ) , but can not rule out circular orbits at high inclinations .
Given our astrometry we discuss formation scenarios of the GQ Lup system .
In addition , we detected an even fainter new companion candidate to GQ Lup , which is most likely a background object .
We also updated the orbit constraints of the PZ Tel system , confirming that the companion is on a highly eccentric orbit with e > 0.62 .
Finally we show with a high significance , that there is no orbital motion observed in the cases of the DH Tau , HD 203030 and 1RXS J160929.1-210524 systems and give the most precise relative astrometric measurement of the UScoCTIO 108 system to date .