If the trunk at the split seems healthy -- whitish wood, no discoloration or hollowness -- they should be okay. If you want to, you can "splint" them back together and bind them with masking tape, and they may very well heal back together. Otherwise, you can probably leave them and let them heal naturally (they'll always have the split there). It won't kill the plants.

Tomatoes are tough, and survive a lot of abuse pretty well. They heal fast, too. The weight may have done it, if the stems look healthy inside... consider getting a couple of trellises, or heavy-duty concrete-wire cages for these guys, or at least for Yellow Pear. YP is a pretty big plant, and it can be difficult to get to all of the fruit if the plant is sprawling.

--Alison
who once had a dog trample a plant and split the trunk when it was bent -- a month after splinting it, it had healed back up and showed no sign of injury. Amazing plants.