pttl and slave flash

I am looking to buy two cheap slaves and what i don't know by now is if a slave flash will work with pttl?
To be more specific, Pttl lights two times and the second time is the one that lights the photo.
What i am wondering about is Will the slaves light two times so they will light when the picture is taken?

A normal optical slave will be triggered by the PTTL pre-flash. However you can buy optical slave units that can be set to ignore the pre-flash by adjusting a setting on the side of the unit.

It's actually not that much more expensive to buy chinese knock-off radio triggers, eliminating the whole issue - unless you absolutely need a PTTL flash on the camera as well.

For example..?

Since you ask sooo nicely

Seagull SYK-5 type optical slave

Cheap wireless radio triggers

Thanks!
Do you know how i could use something like this and also have a flash mounted on my camera?
If the mounted flashes have pttl, will the pttl work?
Can the whole system be triggered by two or more cameras?, How?

I would do a research but my time is extremely limited right now, so this help is very important to me, Thanks.

Regards,
Petros

The flash mounted to the camera will work in Pttl, but flashes using optical slaves or simple cheap triggers will not. For this sort of multi flash set up, I would go with manual flash. It only takes a few moments to do a test shot and adjust the flash output or camera settings.

If you had the monies, three pttl flashes capable of being triggered wirelessly by the camera (e.g. Pentax FGZ360) would work in pttl but meh, better to have manual control anyway I think. That's just my personal view though.

What shoot set up do you have in mind, by the way?

A friend's small Wedding who does not want a photographer but his relatives do, so they said
"Let's give a camera to a cousin to do the job".
But they thought that it wouldn't be nice for the cousin to "loose" the wedding, so i will do the shooting as that's what i begin to do lately.
I have only shoot wedings as a second photographer with the boos's equipment wich i wont have there.
And since i am generally interested in shooting weddings/other events on my own and summer in Greece is full of weddings/events, this is a nice opportunity to begin to build my lighing equipment.