You need to reduce her numbers advantage. No two ways about it. Raising a hand you beckon her to come at you.
"HUH?!"
"Come at me like you mean it Big Mom! I won't stop if you don't take me seriously!"
"Y-You..."
Her voice cracks.
"YOU DON'T MAKE DEMANDS OF ME WHELP!"
At least she got mad. And now it looks like she'll do exactly what you asked of her. She jumps on top of Zeus and the happy little cloud turns into a big swirling mass of blackness with a maniacal expression.
"PROMETHEUS!"
"Yes Mama!"
The sun rests on top of her and becomes a raging inferno which doesn't hurt her and his usually cheerful face gets replaced with two small and one big black void where his eyes and mouth would be. And reflecting her rage Napoleon turns from a longsword into an even bigger seax.
Not wanting to fall behind you also take out your own weapons. Both of which change shape. They grow massively to fit into your hands and take on bat motifs, like Argents crossguard and the spiral patterns of Parley which both turn into various bats, as if the totemic power of your devil fruit is seeping into them and imbuing them with power.
"I was always bad at this. Let's hope you can handle it better than me."
https://www.youtube.com/watch?v=IYOf5DPBX8I Focusing your haki into your arms your weapons turn black as you jump into the fray with Big Mom. The black cloud around you grows thicker as you release more of your hair into the air. To the naked eye it looks like you break up into a flock of bats when you move, with one crimson one leading the horde. This is but a trick of the mind as it struggles to pick up what's going on in the fog, with the red bat being your red glowing eye.
Mama also starts flying at very high speeds but thanks to her vibrant outfit and blazing hair she's much more easy to make out in the bad visibility. You exchange a few blows with your swords and sparks fill the sky every time you clash. Using the Red Voice you try your best to keep up with Mama but she's much faster than one might think. She might not have fleet footwork but Zeus flies with the speed of a squall. And she could be a deceptively fine swordsman, or it could be that Napoleon is attacking you autonomously. It doesn't really matter. What matters is that despite moving like a flash from one spot to another you can't catch her off guard and in a pure contest of strength she got you beat.
As you clash once more you get locked in a struggle and she lets go of Napoleon with one hand only to punch you in the gut with it. Even with the supreme endurance and healing the awakening gives you the punch still felt like it went straight into your soul. But you won't let her have all the fun. Recovering with an exertion of willpower you get back up and headbutt her over Napoleon. That was enough to make her back off a little.