2: Make a trigger covering the whole playing area, activated by Resistance/Guer. In the Condition field, write:
{alive _x} count units thisList < 60
(supplanting 60 with whatever number corresponds to "less than 70% left"). Then just add whatever lose code you want in the On Activation field.
1: It's easy enough to make a sitrep of LIVING soldiers, but a lot harder to make one which differentiates between living and dead

I.e., how many casualities. That is, unless each group has exactly as many soldiers - which I doubt. Also, this would obviously not be voiced, unless you get really creative with the voice acting.
Just reporting living (called just before the actual join, so that there is still a 'leader' for the group):
(leader joinedgrp) sidechat format ["This is %1, joining you now. Our strength is at %2 men.", joinedgrp, {alive _x} count units joinedgrp];
As to reporting casualities, well. What you'd have to do is initially, at the start of the mission, count the number of soldiers in each group. You could either do this with a global array, or by for instance giving each member of the group a vehiclevariable with the information (each member because you never know who's going to die). After that you simply use the above code to count living members, and grab the amount of original members from the array, and hey presto. Here'd be the vehiclevariable one:
(start of mission, in e.g. group leader's init field. Untested):
{_x setvariable ["SAST_GroupSize", {alive _x} count units (group _x)]} foreach units group this;
(when joining):
(leader joinedgrp) sidechat format ["This is %1, joining you now. Our strength is at %2 men. We have had %3 casualities.", joinedgrp, {alive _x} count units joinedgrp, (((leader joinedgrp) getVariable "SAST_GroupSize") - ({alive _x} count units joinedgrp))];
Of course, this line doesn't make any sense if the group hasn't had any casualities, which means you'd have to make an extra check for that and so on and so on. It gives a nice feeling to the mission, of course, but it is a lot of extra work too

Hope these instructions make sense - wish you luck!
Wolfrug out.