what about label?

 <group col="3">
        <field name="x_KundeHatBestelltUndGekauft" /> <label string="" nolabel="1" />
        <field name="x_Brand" /> <label  string="My text 1" nolabel="1" />
        <field name="x_Brand2" /> <label string="My text 2" nolabel="1" />
 </group>

-also there is another option for first field(x_KundeHatBestelltUndGekauft), you can use  colspan="3" instead of empty label, because we made <group> width 3 with col="3" and as we haven't label for first field, it'll fit correctly group width with colspan="3"

        <field name="x_KundeHatBestelltUndGekauft" colspan="3"/> 

UPDATE:

for your issue of distance, you can manipulate column count in group tag and simultaneously use colspan property in fields/labels. take in account that "field" need 2 column space by default. so for each line (for each field & label couple) you'll need to have sum of columns equal to col property of wrapper group tag. for example change above group as follows:

<group col="6">
        <field name="x_KundeHatBestelltUndGekauft" /> <label string="" nolabel="1" colspan="4" />
        <field name="x_Brand" /> <label string="My text 1" nolabel="1"  colspan="4" />
        <field name="x_Brand2" /> <label string="My text 2" nolabel="1" colspan="4" />
 </group>

fields width 2  +  label width (with colspan) 4 fits exactly group width 6.

you can use different numbers, adapt it to your requirements.