There are some varible (manually controllable) props used in electrics but no Constant Speed props as such and typically used on full scale aircraft. That would require engine govenors to alter pitch as loads increase or decrease on the propellor such as climb and descent. Actually if it was avaliable it would buy you nothing with our aircraft never in extended climbs or descents.

Mixture control actually is avaliable on just a few engines such as my rear exhaust Rossi used in a vintage type pattern plane. Agine this is almost perfectly useless with the minor exceptions of certain type venues such as above or a situation I have run into in my XC flights in the past and that is the enrichment of the mixture due to changing elevation along the route of 3000 feet and of course that is predicated by the route choice.

If you want to do a multi, great it is educational, a challange and fun. But first make sure you are proficient in single engine airplanes first and your first twin should not be a scale type but something more appropriate of which there are more choice out there now than ever or kit bash a simple twin which is my favored suggestion to folks who want to get into multi's.

The addition of both the above features to a scale multi is virtually useless in most cases and actually could be detrimental due to the overfocusing on such things when there are more important considerations.

John