thoughts about symbiotes

I fully admit to being a card-carrying, pocket protector wearing, sci-fi watching, vampire loving nerd. Which is prolly why I want to write paranormals in the first place, I mean it can't possibly be a coincidence that what essentially amounts to aliens who used quantum theory to come to earth invaded my head right??

Basically I am trying to figure out the low-down on my pet aliens, and since they like to change their minds its been a little hard to pin down but here is what I know so far
1) There are two (Dax and Adrianna) that came to earth in the 19th century, they opened a wormhole onto Earth to escape their dying planet, Meridia
2) Meridian's don't eat, they actually draw energy from other people and living things, making them kinda like energy vampires (and yes their favorite form of energy transfer is sex)
3) They used their knowledge of electronic technology to support themselves during the Industrial Revolution and hold a few patents on some pretty important but largely taken for granted tech
4) Dax fell in love with an English governess, Emma, sometime in this period, shortly after Adriana joined some kind of English exploration company so that she could explore the world
5) Humans with Psychic ability are genetically compatible with my Meridians so within a few years Dax and Emma had about 7 kids, all combinations of Meridian and Human DNA which gives them unique issues.
6) At some point Emma suffers a traumatic injury and Dax gives her his blood as a transfusion, altering her enough that it amplified her physic powers and gave her a life span closer to that of a Meridian, who usually live between 5 and 6 hundred years and are resistant to most things that kill normal people
7) the half-Meridian's (Emma now included) have some pretty particular issues.:

• with food and digestion, their bodies won't tolerate anything "dead" so the eat a raw veggie diet.
• They can handle inorganic matter (things like medications and preservatives) but not usually in large quantities.
• They are also deathly allergic to Tylenol, and have to be very careful about vitamin regiments to stay healthy.
• Sunlight tends to burn their eyes and their skin becomes very susceptible to burns.

All good right? but what is plaguing me is how to make these changes work, DNA is great for the kids but how do you explain the blood transfer??? it's kinda complicated but I was reading about E-Coli and how it lives in a symbiotic state with humans, infecting them shortly after birth and then protecting them from all other forms of E Coli thereafter and I was wondering if this might be my answer, cause I do love a good symbiote (What Up Teal'c!!)

BUT I worry that I am adding into much, I already got aliens, magic, quantum physics and I don't want to overload people with Sci-Fi outta the gate ya know? Anybody got any suggestions for me???