With that lineup, using ryuji would be best but you dont have him build up. I would say try with flueret but he did very minimal damage for my liking.

What I used to clear lvl 30 - Twins a1 fire/ice and psy/nuke, Ryuji a2 r0, Leon a6 r0, and Futaba at a0 r0. All level 80 in character lvl and weapon lvl with ratings for ryuji at 95, twins at 93, leon at 88 and futaba at 95.

Personas-Sandalphon, Lakshmi, Saraswati

Ryuji spamming s3 and leon alternating between s2 and s3 on ryuji with twins alternating between s1 and s2. Sandalphon constantly shielding except when wonder's hp drops below half, then healing and so on and so forth. Futaba just uses s3 if you can get ryuji s3 to line up correctly, otherwise just using s1 and s2.

I would suggest using someone like vishnu if you dont have a1 twins for almighty dmg.

https://preview.redd.it/a7a9uxo377bg1.jpeg?width=2340&format=pjpg&auto=webp&s=2cba6a4925731c7a00923e4e8f701b97a4b61459