I know better than this but I mixed a off brand and a name brand drain opener. As soon as I did this the gases started filling up in the house and before I knew it my whole family was coughing, eyes burning and we couldn't breathe. We evacuated the house. How long should my family wait to go back home

It would depend what kind of gas it produced... maybe call poison control and ask them, they should know the major brands and how they might interact.

The gas will not necessarily dissapate that much on its own. Open all exterior doors from the outside and let the home vent for at least 12 hours. Can you tell me which 2 cleaners you mixed?

I know better than this but i mixed a off brand and a name brand drain opener. As soon as I did this the gases started filling up in the house and before I knew it my whole family was coughing, eyes burning and we couldnt breathe. we evacuated the house. How long should my family wait to go back home
Open up your home, rent a couple of ventilating fans and air your place out. How long it will take will depend on the size of your house. As a repair plumber I have never recommended using harsh chemicals.in your drainage system. Besides they only seem to work in TV commercials and when you try to remove the water you could burn your hands or damage your eyes.
The only sure way to remove a clog is to snake the drain line out and then flush the mess out. To snake a drain line you first remove the "J" bend from the thap and send your snake up into the wall,(see image) On sinks and lavatories/vanities you won't have to put out much over 6 feet.
Good luck and thank you for ratting my reply. Tom

Yes, my family has been in the plumbing business for years, and they always add a extra service fee if you used that in the clog before you called them because of the added danger working on the pipes.

Personally don't use them, clean it out properly.