The first time I tried this I was afraid too.
I never heard of a lifeline... I might try that now too.
However, I have now knit up to 4 strands together, even 4 bulky weight strands to make my hubby a car seat "cushion" which I made with 4 strands knitted together of Lion Suede which is 5 ply or bulky yarn. So far, he has found 3 errors where I didn't quite knit in one loop of the 4 strands... and they are easy to fix for I just use a plastic needle found in yarn depts and "sew" it down. The cushion was made 22 inches by 18 inches, and the strands never even ran or moved.
Just go slow and make sure you catch both yarns in each stitch. Once you start getting the idea, you'll speed up some too.