look up "Cimex" (bedbug) on the web, and see if that's what you've got.
That would be a cause for concern for your family; ticks would really only be a concern for your cat.
it could possibly be ticks or mites.
Lice are fairly uncommon in cats, but cats that are in poor condition, or extremely young or old can be susceptible.
Lice are species specific, so cat lice generally do not spread to humans, dog lice generally do not spread to cats etc.
Cat lice can be seen fairly easily with the naked eye, as can their eggs or nits.
There are three types of lice that can affect cats, two of these bite the other is blood sucking.
The tell tale signs of these cat parasites are scratching, although not necessarily excessive scratching, and a drying of the skin showing an increase in scurf or dandruff.
The eggs of the louse are laid directly on the hair, close to the skin, and adhere tightly.
Since it is a stray, you'll want him vet checked asap in case he needs medication for anything specific.