Is it ok to put your Ancestors' pictures on the altar?
Yes, or also around the house, it's also a good custom for Samhain (known as Halloween).
Between our Ancestors there are also the Gods, and the Zevists of the past, known and unknown.
Maybe also having something general for all, is good.
Like that custom (it was Roman if I remember) of having an altar to honour all the unknown Gods, like many of the Minor Ones.