My little girl is turning mean...

How is it, was she always nasty to your husband, or is this something new?

if it is entirely new, it may be stress of some sort, or even something hurting her. Cats in pain dont have their usual patience.

Is your husband cat friendly??  Some arent nasty at all, but they speak in a much stronger voice, and so on...

Anyway, Feliway diffuser is a good try.

The main weapon in such cases is although, let your husband give her food and treats, and clean the litter, as often as possible.

Very effective is if you stay away some days now and then, and your husband is the only one with the cats... Perhaps even taking leave from his job...

Several days together, with only him attending the cats, is a very powerful trick!

So, combine this trick + Feliway, and it should be OK.   :)

Clipping nails may be tricky.

Holding the scruff off the neck is one tip.

One holding tight in the arms, holding the cat down with the chin, and the other doing the clipping is another.

If it is difficult to take all the nails, take only some. Say one paw at a time. And let her go before she is tired.

In difficult cases it often helps to wrap them up in a bath towel.  This way they are helpless, and being helpless, they  become submissive.

Describe your technique, it will be easier to give advices!

Good you are taking all the introductions slowly at their pace... Toghether with the same Feliway should go well.  Although many strays try to adapt to residents so often there arent big deal from theirs.

Good luck!    *vibes*