To answer your question about making the instrument less bright - that can be done quite easily with the low-pass filter. Go to the instrument tab and look for
Filter, cutoff (Hz). That refers to a lowpass-filter with a roll-off of 12 dB per octave: the sound frequencies above the desired amount will be decreases in amplitude with 12 dB per octave. Values within
Global affects all samples of the instrument, otherwise the value affects for the samples individually. You can see what it does on these images representing a spectrogram views of a cello sound when a lowpass-filter from 4000 Hz with a 12 dB roll-off is applied.
Start with a value of 4000 or 5000 into
Global and find out if it is what you want. otherwise you'll have to use another value.
About the vibrato. In general the vibrato of a sampled violin is recorded into the sound file itself. Check if that's the case by listening to the samples.
Otherwise the vibrato is programmed into the instrument-settings. And then it's possible to delay the moment from when the vibrato appears.
A vibrato can be programmed with
Vib LFO or
Mod LFO into the instrument-settings.
Delay refers to the moment when the vibrato starts.