In most cases you can use both XLRs and Jacks together.
One thing to watch out for is that if the jack plugs are in fact balanced TRS jacks they could be wired directly to the Balanced XLRs. So if you plug an unbalanced jack into the balanced jack you will link pins 1 & 3 on the XLRs and unbalance everything. It will however probably still work only unbalanced.
Some mixers will have balancing transformers on both outputs so in that case plugging an unbalanced jack in won't unbalance the XLRs.
Hope that was as clear as mud LOL.
Alan.