The legality of blockers being in the line of sight of a passer really comes down to whether or not they moved to get in your way. Most teams try very hard to make sure that there is at least one person between the opposing passer and their server to give themselves a better chance at throwing off their opponent’s offense, and that’s acceptable.
This situation becomes a problem when the serving team watches you and actively moves around to get in your way.
So a team can have their front row players (and back row, for that matter) set up in whatever way seems best to them as long as they’re in the right order/rotation. But if these players move around for the purpose of blocking the view of the passers then they’ve committed a fault ad you should get the ball.
If you’re having a problem with the other team screening but the referee doesn’t seem to be noticing, try to exaggerate the problem by moving your head dramatically from side to side as you attempt to see around the other team’s blockers. Hopefully the ref will notice this and take note of whether the other team is actively blocking your site of the server. If s/he doesn’t notice and you’re in real difficulty ask your caption to speak to the ref.
This can’t be called on a server, however, and they can move around wherever they want to make your passing life more difficult. Many servers like to position themselves behind as many of their teammates as possible for this precise reason, and that’s legal.
Good luck with your serve receive efforts. For an illustration of referee calls for screening, visit volleyball-life.com.