11.1 and 7.4 lipo combo
 

Can I combine these 2 voltages in lipo for my 18.5 volts as long as I keep the mah the same without any problems?The combo I want to use is the feigao 8xl with the mm esc.

Yes, it is ok to series connect packs of lipos as long as they are of the same Ah capacity, as you stated. It is also advisable that each pack have the same number of runs and general usage. Preferably, they should be bought together, used together, and charged together.

Make sure to wire in series; parallel would cause bad things.

You should be fine as long as it is not a big difference in runs and age.