Your situation is not uncommon after multiple C-sections, and actually is an excellent demonstration of why abdominoplasty, or tummy tuck, incisions are positioned low and horizontally, and not vertically. The low horizontal incisions generally heal much better than the vertical incisions below the belly button. Multiple pregnancies are usually associated with an excess of loose skin and some bulging of the abdominal wall muscles which could be improved with tummy tuck surgery. In fact, the "ugly" vertical scar could probably be completely removed and replaced by skin from the upper abdomen, which would be pulled down and tightened. Although plastic surgeons try to make the scar as small or as short as possible, the "bikini cut" scar that you have would need to be lengthened in order to prevent redundant skin from puckering on each side. The incision would probably extend from hip to hip, but again, it would only be as long as necessary to make everything smooth. This scar should be low and hidden by lingerie or even bikini type swimsuits. If your 4th C-section healed well, then a scar of the same type and location should heal just as well even if it is a little longer.
There are many types of abdominoplasty, or tummy tuck, operations that are performed, and it is impossible to know exactly which variation would be the best for you without an examination. It does seem by your description that you would be a good candidate for a full tummy tuck with an incision around the umbilicus (belly button), tightening the bulging abdominal wall, and removing the vertical scar and excess skin in the lower abdomen. The skin from the upper abdomen would be tightened by pulling it down to leave a low horizontal (bikini cut) scar.
