You would plant the two watermelons next to each other, but both will (probably) need enough space for a melon (2 feet apiece for a vining type, 1 apiece for a bush type - I don't know what these are.)

A tomato "sucker" is a new branch that grows in the axil where the compound leaf meets the stalk. Have a look here at a tomato leaf's anatomy.

Generally, you only want to trim suckers from an indeterminate (vining) tomato - trimming them from a determinate (bush type) will drastically affect the yield of the plant.

Here is a link that might be useful: How to prune tomatoes

Hi crystabel
I don't know about your watermelon question, but i will answer your tomato question. That was precisely my question a few years ago - "what the *&^% is a sucker?"
Basically you want to make sure that your tomato plant grows straight up along one stem without branching out too much. Once the plant is about one or 1.5ft tall you will start seeing the suckers (perhaps 2-3 weeks after planting). Pay attention to the joint between the stem and the leaf branches (leaf nodes i guess) - you will see little leaves growing there - if you let them be, they will become a new branch. You want to just pinch them off, so that the plant focuses on growing straight up.
Gosh, it's so much harder to explain - when it will take 2 seconds to point out what a sucker is.

Good Luck. Try googling tomato suckers, you will find pictures i am sure.

was just looking around for this information, and found it. Granted, you probably figured it out in the last year, but no harm in posting for the rest of my newbie friends who might be interested ;)