For the "Fearsome Super Elite" stages its easiest to use the best TEQ team you can assemble
For 'The Final Showdown' you have a cost restriction on your team. This leaves you with 2 main options. You can either build a team with a really low cost and have one TEQ 'nuker' (really high Super Attack hitter) on the team such as Perfect Cell - Surpassing All or Super Gogeta - The Supreme Warrior with Ki boosting support items and captains to try take him out in a couple of blasts before your hp hits zero.
Or if you don't have a nuker and none of your friends have nukers you can try put together your best TEQ team that fits under the 100 team cost restriction. You should use +2 or +3 Ki Booster captains to get as many special attacks in as possible. Use your best support items like full healers or enemy turn skippers. This way isn't impossible but its very hard and you might need a certain amount of luck. Below is a team we put together that just got us through. It's not over the top and you should be able to substitute the ones you don't have with something similar and get the same results. We used a +3 TEQ Ki friend helper and for support items we used sensu beans, Dende full heal, Cargo 25% heal and one that skips the enemies turn.
Try pick characters that will link up for extra help. Here we used super saiyans because they have good link skills.