lol got ya, ok...first things first, start tw companion quest line, when you finish the quest into dustmans cairn the next one you start is called "the silver hand" ok, that's the quest where you become a werewolf. At this point go start the dawnguard quest chain, doesn't matter which side, one just takes a little more work, if you pick vampire, you will have to cure your vampirism via the guy in morthal, and if you pick dawnguard your good to go. If you pick the vampire side, which I did, it is IMPERATIVE that you WAIT until after finishing the "prophet" quest, because once you do this you don't progress in stages of vampirism anymore, which is essential to have vp seduction to complete the quest, and if you do like I did earlier today, you will waste 4 hours of gameplay to realize you have to do it over again -_- lol always save before attempting weird stuff lol
Ok, here's the tricky part...1: assuming both earlier stated conditions are met, go to the under forge and wait til dark to talk to Skjor, once you do he will walk into the under forge.
2: at this point have serana turn you into a vampire lord BEFORE walking inside as she can't follow.
3: after Skjor asks you if your ready say yes, get your vampire lord powers to your action (Right Bumper) button, when you have the option to click on the fountain of blood, hit the A button to accept AND the right bumper at the same time. This triggers the quest progression AND the vampire lord transformation at the same time, when your screen comes back you will be in werewolf form and immediately burst into vampire lord form.
4: here's where time is precious, immediately revert form back to human, then talk to serana and have her turn you into a vampire lord again, it makes the change permanent. Then access your beast form from your powers list and use it immediately to turn back into a werewolf before you black out and the quest progresses.
5: when you come to, you will be outside the silver hand fort, and possibly have a odd shell like thing over you that looks like the werewolf body, only had that happen once, but either way, at this point, it doesn't matter which, just use either the vampire lord or werewolf (gotta wait 24 hours) form and it will go away...
And there ya go! You have both abilities, both perk trees, you can continue both quests like normal. For all intensive purposes you are considered both a vampire AND a werewolf, I have received comments "your skin is as pale as the snow" "don't like those eyes you got..." "have you been taking care of the animals or something? You smell like wet dog"
The only thing that's noticeable is this, no weakness to sunlight, no vampiric progression, no vampiric drain spell, no beast blood debuff to keep you from getting the rested bonus, also, you keep the Passives of the last transformation you did, so if the last you did was a werewolf, then you will have resist disease but not resist poison, if vampire, you will have 2 instances of resist disease, one for beast blood an one for vampiric blood, and the vampiric blood for poison resist. You can also use the ring of hircine, you can use the face sculptor in the ragged flagon (couldn't if you were a vampire before) and you still retain the necromage bonus if your speced into it. All tested and working, no problems with either transformations or interactions...it also works really well together for raiding forts (especially the ones that repopulate with imperial/stormcloak soldiers after clearing them) to Go through and kill them all with the vampire lord powers and get the perks, then go back over the dead bodies and feed on them as a werewolf to increase its perks, your also considered friendly to the WEREBEARS in Solstheim, so you can buy the other 4 rings from them. And you can continue and finish the vampire side of the dawnguard quest chain with all appropriate dialogue including the fitting comment by harkon during kindred judgment where he says "you would choose this...half breed? over your own family?" of course in reference to you not originally being a vampire lord but hey it works lol