While I don't, currently, have any citrus, I have had many in the past. Although I was a chemistry major in school, I have never really had much concern about the pH (maybe I should) My citrus have grown good in the mix that I use for just about everything. This is a third each of peat, perlite, and compost, plus time release fertilizer, (like Osmocote, or Polyon) wetting agent, (like Aqua Gro) and water retention crystals. (like Soil-Moist) This whole thing is mixed with recycled old mix, half and half. If I suspect a problem, (like chlorotic looking leaves I'll do a test. Currently, I have banana, pineapple, guava, passion, pomegranite and carambola.

"pH (around 4.8 to 5.0) Is this too acidic for these plants?"

Sounds pretty darn low, in general.

google around with multiple terms like "plants minerals acidity pH", lots of general info.

then add in "myplant acidity pH" for specific info.

where myplant is your type of plant.

Citrus like fairly neutral to mildly acid conditions, they tend to develop iron chlorosis if the soil pH is too high; Oleander is more tolerant, but prefer a relatively high pH (I assume you are referring to Nerium and not Thevetia, I know little about optimal conditions for the latter).

Ryan