servant synergy team help

That picture is tiiiiiiny. Can't see levels, but at least the faces are clear.
You'll want to focus on having at least one leveled up servant for each class. Based on that picture, I'd recommend:
Caesar, Robin/David, Cu Chulainn, Ridertoki, Medea, Kotaru/Kojiro, and Ibaraki

After that, you can start looking at synergy for more difficult things. Keep Mash up to max level, and get Andersen, Medusa/Alexander, and Caesar up to snuff.

For basic synergy, look at what style a servant is. For instance, Ridertoki is a powerful Quick-oriented character who would benefit a ton from the added crit stars from Kotaru, or the Quick card buffs from Alexander. Riders and Archers are greedy with crit stars, so supplying lots of stars for a single Rider or Archer in your frontline is ideal.

Another synergy would be Mozart/Robin. Mozart's buffs to Arts cards and ability to supply crit stars for the Archer help Robin do real damage outside of his NP, but also brings his NP into dangerous levels of damage. Mozart's kind of a one-trick, though, and Andersen can be just as useful in more situations.

NP spamming characters like Medea work well with Andersen or Mash, or other Arts-based characters.

Buster-oriented characters like most Berserkers love characters like Caesar, who help their Buster cards or their base ATK. Ibaraki/Caesar would be pretty effective together, with maybe a friend's Waver or Helena to help their NP gauges and damage.

Who do you enjoy using the most? What problems do you find yourself having in the singularities?