I have a very good technique on into the belly of the beast that works wonders for me. I've come out of it even with marine survivors, but I was lucky on those occasions.
Firstly, you should have a sniper rifle with full ammo and either a plasma rifle or AR. If you threw your Sniper away, you're a complete idiot and want to do things the hard way. Kill the first sword elite before he can kill any of your men. Whenever a door opens, toss a grenade at the entrance and let your marines take care of the grunts and jackals. If a gold sword elite comes out, focus all your fire on him. It should take about 3-4 sniper headshots to down him, or one well placed stick. Get his attention on you so he chases after you in a straight line, amking for easy headshots. Always focus on killing the elite, your marines can handle themselves and divert fire away you from the grunts. It's the elites that can decimate your squad in a few seconds.
After all your marines are dead and you are about to be overrun, grab the invisibility. It takes a few seconds to work, so wait until a moment BEFORE the last possible moment. Go around whacking all the enemies on the back and sticking them, but not shooting. Then go down one of the corridors to get cover. You can take out the enemies in here and lure any remaing elites. Once the hunters come, use the corridors to flank them and snipe them in the back.
I managed to survive into the belly of the beast without even having to go for the invisibility or health pack, with two marines left. however they instantly got killed when the hunters came. I was quite lucky though as I did not get many elities.