Dual zone vs single zone mini split Air/heat
This skates awfully close to a shopping question - but. What I have observed in my consideration of the same question is that the most efficient units are essentially always single-zone. This makes a degree of sense, as an outdoor unit that can run 2 (or more) inside units will be oversized when less than the full number of units are calling for service at the same time.

That is treating the running cost as a prime motivator (which I do) - purchase cost can be and is all over the map, but is more often in favor of a multi-zone system.

The factor of not having a single point of failure for the entire system is also a consideration, as @Jim Stewart points out in a comment. Systems do fail or require maintenance, and there's a big difference between everything not working and half of things not working when that happens.

If you have no A/C now, your electric bill is hard to predict, considering no information about insulation (probably bad at that era unless it's been upgraded) and sun exposure. If you use window units now, very probably the cost will go down, so long as the mini-splits are more efficient (higher SEER) than the window units. 

I note that only one of your brands expresses a SEER number as you're presented them to us. You should find out what the other one's SEER rating is, as that greatly influences the cost of operation.

Relative cost of heating with the mini-splits .vs. propane will depend on the price of each fuel and efficiencies.