IBKR Fractional shares order type & double orders with double commission

1. It looks to be available on mobile app. You can refer to this article for the detailed steps to take to execute as such: https://financefeeds.com/interactive-brokers-mobile-app-enables-fractional-share-trading/
2. Based on IBKR website: https://ibkr.info/article/3416

What order types can I choose for fractional trading?

IBKR will only accept certain types of orders for fractional shares (e.g., market orders, limit orders, stop orders, stop limit orders, etc.). If you choose to place an unmarketable limit order with a fractional share component, the fractional component may not execute until the order becomes marketable (and therefore may not execute at all), even if the order might have executed earlier if submitted for a whole share quantity.

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I think you'd better check with a representative.

1. I always use IBKR PC app for fractional shares trading, not sure about how it works in mobile app. You should check with IBKR on that.
2. Yes, it is normal. Fractional orders can only be with market orders, probably more challenging to fulfill the limit orders in one go, as the prices for the whole and fractional portions would be different (with the fractional prices less favorable and hence more difficult to meet the limit price).