My toilets do not flush well; bubbling action and then most of the times have to flush a second time. Sometimes the water from the guest shower backs up into the master shower and then toilets would overflow. My septic was pumped out two months ago. I was told that if there was a blockage, the excess would come out of the overflow at the front of the house. This has never happened but the backup happens in the house. Please any advise would be appreciated.

Your blockage is in the house not out at the field or tank. The bubbling also tells me your vent stack need to be looked at and probably snaked. Rod the vent from the roof to basement floor plus 20'. Look for a clean out in the basement on the drain line. DO NOT REMOVE this clean out because we do not know which side of it we'll find the blockage. Drill a tiny hole in the clean out cap the size of a self tapping screw you have on hand. Flush your toilet, ifwater shoots out of the small hole your blockage is further down stream. No water means the block is up stream in the home. Down stream, rod from the clean out. Up stream rod from any other cleanout or major drain. You could even pull the toilet if you have to. Before I forget, put that screw into the cap with a dab of plumbers caulk on the threads.

I do not have a basement. I have a overflow pipe outside of the house (I have septic). I opened up the overflow and had someone flush the toilets in the house. The water came out but then it sat there. I also ran the shower and washing machine, the water came up but at no time did it overflow outside the house. Should I snake out the vents on the roof? Any assistance would be appreciated.

Reread my post #2 . Yes vemnts could be blocked but I still think you have a drain pipe problem inside the house. If you want, rod rppf to basement floor plus 20'. If the problem still exists do what I said in #2