oh yeah, another group of people that were probably a part of this same group are Isaac and Julia Laflorenze, and the two that fled with Isaac to Dracula's castle in the manga. Isaac and his pals were shown to dress very much like the gypsies in Simon's Quest. They may not be close relatives to Sypha Belnades, but probably of the same "people" or "clan" even. We know that Julia escaped the witch trials. Isaac and his companions were shown fleeing the church in the manga, probably for practicing forbidden arts that would be common among their people, and decided the only place they could be safe and accepted was Dracula's Castle.
another potential candidate is the witch Drolta Tzuentes in Bloodlines. again, she's covered completely with robes and a hood and she fights (it appears as if she is Dracula's 2nd form) exactly like a Carrie's cousin, who was at least related to the Belnades family and was originally intended to by Sypha herself brought back from the dead. we don't know her motive for resurrecting Elizabeth Bartley and Dracula, but possible retribution against what was done to her people could be a part of it and its possible their persecution continued into the 20th century. she could have become Elizabeth's servant ages ago willingly or might have been sired by her. there's also a witch in the Rampart stage of The Arcade who fights like Drolta and Carrie's cousin. perhaps all three are the same person, a vampire Belnades witch servant to Elizabeth Bartley?
another witch is Actrise, but her background, dress, and fighting style (crystal based) seems to be different than the gypsies or Belnades, and her power seems to come directly from Dracula rather than nature or spirits. the general fighting style of the regular witch enemies in Castlevania also seems to be different, perhaps because they're more of the "Salem" variety.
its interesting how some gypsies chose to side with Dracula and some decided to oppose him. Sypha recognized that evil forces like Carmilla were behind and at least escalated the worse of their persecutions.
UPDATE: Oh, and then there's the Ferryman. It's interesting to think of him as the ghost of one of these Gypsies, who guides adventurers over the centuries around waterways outside, to, and inside Dracula's Castle. Again, he dresses in the same hooded cloak that the other gypsies do and is shown to do so in all games he's been in. So does the "old crone" merchant who appears in Vampire Killer (interesting that she also deals with Hearts as currency) and the horn-playing druid in Castlevania Chronicles. It's possible that also that the mysterious merchant from Harmony of Dissonance is one of these people or one of their ghosts (he lacks the hood and accepts coins instead of hearts, but so does Julia).