Since each pair of injectors is retained with one bracket, they are best worked on as a pair - i.e. remove a pair of injector lines at both ends at a time. Whatever your procedure, do NOT bend the lines at all! It will be difficult to reattach them without crossthreading if you do. Also, the reason for squeezing both wrenches in one hand is it prevents inadvertantly putting undue force on the retaining bracket and damaging it.
Using a single edge razor blade to slice the old seal should be fine, using safety precautions and cutting only far enough to insert a flat-edge screwdriver tip. That you twist to propagate the cut until the seal is separated.
'91 MB 190E 2.3
'08 RAV4 Ltd 3.5
'83 Lazy Daze m'home 5.7