Question: Gardening in Abu Dhabi

Hello fellow expats. I am from the US and consider myself a pretty experienced gardener. Problem is the soil Ph, type, and humidity here are much different then where I am from (North East US). My begonias are all dying...and they are normally very easy to maintain (hardy plants). I looked up some things and it said it may be a fungus or bacteria and to wipe the wilted leaves with rubbing alcohol....pluck affected leaves ASAP...etc... none of that is working. Half the plants are thriving and the other half are dying. None of them are in full sun all day (because they don't like that) but they do get an adequate amount a few hours per day. I let the top soil dry before the next watering...because they don't like to be soggy (attracts bacteria), which amounts to once or twice a day. Is this NOT the correct way here?

Normally I would not try anything that was not native to the area for my first attempt, but ...well...it's the desert....there is not much here that is! lol  I can say that my desert rose plants are flourishing Any help would be greatly appreciated. I love to garden and just need to learn the area *)