For each wallet, we will get the provider with rpcProvider, to fetch the balance by calling the getBalance with the wallet address. 
import { useUserWallets } from '@dynamic-labs/sdk-react-core';

const App = () => {
  const userWallets = useUserWallets();

  useEffect(() => {
    userWallets.forEach(async (wallet) => {
      if (!wallet) return;

      // Get the configured rpc provider
     const provider = rpcProviders.evmDefaultProvider?.provider;

      if (!provider) return;

      // Fetch the wallet balance
      const balance = await provider.getBalance(wallet.address);

      console.log('balance', balance.toString());
    });
  }, [userWallets]);

  ...
}