In the key product specifications for each trampoline, you'll find details of the maximum weight limit. It's important to bear this in mind when considering the size of trampoline you need. Typically, the bigger the trampoline is, the higher the overall weight limit.
Take a look at the max weight limit stated by the manufacturer in order to keep play safe and to understand whether you can have a couple of kids, or a parent, on there at the same time with no concerns.