A friend told me that you could pass through Zamorak entrance (to stronghold) with a familiar summoned. So i was wondering is that the same for Saradomin stronghold?

I believe so. It was changed a little after the Zamorak one and was unannounced (at least on the main page, haven't looked at the patch notes).

Thanks

I've heard that you can get them through zamorak's fortress and saradomin's encampment now