Well, joey, he already has the fish, and I don't know what else he could have done but break it down completely to replace all the silicone. I'd have done the same.
Thanatos, look at this as your chance to learn all about cycling a tank. Once those ammonia levels begin to rise, you'll want to check them every day and do the partial water changes to bring it below 1.0, then once it subsides you'll do the same for nitrite. You may think it's taking too long, but you'll hang in there and one week you'll find that both ammonia and nitrite are at 0.
You'd better explain to your family what happens when you add too many fish to an uncycled tank so they'll quit throwing their money away buying unsuitable fish as 'gifts' for you. Tell bil he can get his money back now on the gar, but can't after it dies from ammonia or nitrite poisoning.
Make a stocking list and post it prominently, with a note that adding fish before you say it is okay is flushing money down the toilet because the tank is unstable right now. At least that's what I would do.
Good luck with the family, and with the cycling. You have tools and knowledge at your disposal now.