We have four toilets in the house. Two upstairs on one side of the house, and two downstairs on the other side of the house. When you flush our gues toilet downstairs, the toilet in our master bath gurgles. The toilet that is flushed doesn't gurgle though. My kids have also told me that upstairs, when one of the toilets is flushed the other gurgles.. but again not the one being flushed. This has just started to happen both upstairs and downstairs in the last few days. Do I just need to get my vents flushed or is it something else?

Do I just need to get my vents flushed BINGO!
You have described an venting problem. The gurgle tells me that one toilet's attempting to vent through the trap of the other one. The sound you hear is air being sucked the toilets trap. Get the vents snaked. Good luck. Tom