What did all of those plumbers do to come to that determination? Did they open up the ceiling below to inspect the drain connection or proximity of where the water is coming through the subfloor? I would want to be assured that it really is the shower base as this is going to be very costly to repair properly.

If the shower pan needs to be repaired you would at the minimum need to remove the bottom row of tiles provided the shower was waterproofed properly. What type of pan is it as most times they are not truly repairable? Permits are location dependant and unfortunately shower size means nothing except increases the dollars for the redo.

Your bathroom doesn't look that old - do you know when it was built/renovated?

Hi can you tell me the name brand model number of those shower faucets

Tile showers are often built with no actual physical "pan" that is there catching all the water and can be patched. There are a lot of ways to build a shower and there is no way to know how yours was done unless you tear it apart and ruin it. They trash the entire old shower floor and at least a few inches up the wall, then rebuild it from the beginning.

Now would be a good time for your family to learn about how a tile shower is supposed to be made. There are some good methods, some iffy methods, and some very bad methods, and you cannot tell by talking to a tile person which he is going to use unless you have studied up and learned about it yourself. You can search this forum for "tile showers" or go to the John Bridges Tile Forum online and just read. Learn what the proper ways of building a good shower are. I can't tell you because I don't know all of it. I know that it is difficult enough to find a good tile job that I just won't have it. I went with a solid surface (like Corian) shower. No grout for me, either. Even if your tile person uses the right methods, they have to do them correctly. So read, and learn.

Is there any chance that your house is still under warranty, with your shower being so new? It would be an awful shame to have to tear it all up. Can you explain what the plumbers did that told them that it was the shower pan and not the plumbing?

How about trying a tile and grout sealer: A, B?

Tile and grout sealer does not stop leaks. It prevents stains on the tile and grout surface. Leaks are happening because of things that are going wrong deeper under the surface - or because of plumbing leaks off to the side of the shower pan.