Since the Xenomorphs technically don't have obvious "genders" (even in the films), you have to rely on the body shame and features to be more masculine, or feminine. For females, try tags like 'wide hips, 1girl, female, breasts, curvy figure/slim, etc', and for masculine you'll just have to swing it, consider muscular tags along with "1boy, male" and similar 'masculine' tags. I often view Danbooru and E621's tag wikis for relevant information. Adding genitals helps, too, but isn't always available depending on the framing of the generation.
If you are talking about having multiple characters in the subject, consider using an extension like Regional Prompting, while allows you to specify certain characters in parts of the prompt (Eg. Female Xenmorph on the top-half, and a human male on the bottom half). That's a whole can of worms to get into and learn though.

For the time being I don't have any plans, but I might revisit it in the future and experiment with a 'normal xenomorph' + 'xenomorph queen' lora, where hopefully it could do both types.
I had mostly excluded xenomorph queens because I thought it was going to mess with the normal xeno's heads, which are typically long and smooth.

You might want to re-read the notes section, I wrote shouldn't, not should :p - I was never able to get results myself, since very few people ever actually drew it, and the times people did, it wasn't very detailed or close enough for the training to really pick up on it (let alone be tagged properly...)

As for the dual-xeno question, I've never been particularly good at generating more than 1 character at once, let alone 2 identical characters having sex... I would look into the e621 wiki for tags for same-species sex, or clones, or twins, or something in that capacity. You might be able to cheat, using a sort of 'Point of View'-type prompting, where the viewer themselves are seeing from one of the Xeno's perspective? Using the Regional Prompting extension might be a very viable way to do exactly what you want, although that's a whole can of worms if you don't already know about that extension. I used that extension for the Predator/Alien photo I posted in the gallery below, it's hard to work with, but can give results. Hope this helps, and good luck!

I went ahead and tried to prompt for 2 Xenomorphs doing the do, and managed to get results:
https://civitai.com/images/13791187
I mostly just made sure to prompt for sex and xenomorphs, and no other species; I got this prompt from a random E621 post (using an extension to pull the tag info from a post), and just edited it until there were no other tags than the xeno, and then prompted hard into: "twins, intraspecies, clone, clonecest", which seems to have yielded pretty consistent results. (Note: I barely cleaned up the prompt, so it could probably be a lot shorter, but oh well)
Hope this helps!