Well, in the file briefing.html you should have this:
<p><a name="Plan"></a></p>
<p><a name="OBJ_0"></a>Hold <a href="marker:camp 1">this</a> postition.</p>
<hr>
<p><a name="OBJ_1"></a>Return to <a href="marker:camp 2">the camp</a>.
</p>
Then in the init.sqs file you have to write:
"1" ObjStatus "HIDDEN"
Finally, make a big trigger with name let's say T1 activated by your side and in the other (or in the trigger T1) condition place (west countSide list T1) < 32, where "west" can be replaced by the name of your side (west, east, resistance or civilian) and "32" with a number of 50 % of your units, and in it's "On Activation" field place "0" objStatus "FAILED"; "1" objStatus "ACTIVE"
Add: Don't forget to use commands hint "Objective updated" and hint "Objective done" with a change of objetvives