Hi SydneyB
Midwives can and will do epis at home if necessary, however its really quite unusual to need one for a second baby, unless it looks like it will be a very bad tear. It is usually done at about 7-8 0'clock position, so, yes it may go through the old scar.
Remember that with an epis, you are cutting through the muscle as well and with a tear it is often just skin involvement, so its normally better to have a tear.
The best way to minimise the tearing is to birth slooowly, let the head come out really slowly and there is much more chance of the peri stretching. Give an almighty push as the head comes out and you will probably tear. Also, many tears are caused by the posterior (lower) shoulder when the baby is delivered horizontally, IYKWIM. If you can imagine lying on your back, and once the head is out, you reach down and lift baby up to you, the body will be coming out at roughly 45 degrees, and the shoulder will not tear the peri. (Try getting that through to the doctors though)
When I trained, it was almost routine to do an epis with a first baby, so some older m/w are a bit keen to still do them - the upside is that you get pretty good at repairing them though.
Its really difficult to tell prior to pushing if you will need one, but unless you had very bad tearing last time (so a lot of scar tissue) its really unlikely you will need one. Incidentally, the sutures should not hurt at all if you have good local anaesthetic, (and I know from mn that the sutures can be a lot worse than the birth).
It is cruel and bad practice to have the woman jumping around in pain during suturing, so if its sore, demand more local anaesthetic. You will feel touching in the vaginal area, but you should NOT feel the stitches.
Sorry if this is a bit technical and gory!