What's a good team I can build with my characters?

well you have ssj Bardock and ssj Broly plus kaiyoken Goku and they're all z tier according to this site, I'm not really knowledgeable in team synergy but id just go with that.

To build a strong team you will need your strongest of each color and also they need to synergize each other (Z-Ability/Tags..etc) there are 5 colors, you can get away with 4 color in your team then the other 2 character can be anything that z-boost your 4 main color character so if you are building Saiyan the last two character will be there only to boost Saiyan thru z-ability (Strike damage, HP, etc).

For what you have you can use:
Purple Broly, Kaioken Goku, Red Broly, Yellow SSJ Vegeta then your last two can be EX Blue Goku and EX Blue Raditz (They both have good z-Ability that boost Saiyans, you don’t have to use them just put them there for the ability)

If you manage to get Gogeta, replace Red Broly.

Here is what I’m using:
I could use EX Blue Goku instead of SP Purple Vegeta but I really like the z-ability of Purple vegeta plus he is almost at 5 stars which will level up his z/ability to the next level.