Toilets, Sinks, Showers, Tubs and Disposals - Both Toilets Frequently Clogging

We have two bathrooms in the house, and both were gutted and redone within the past five years. Low flow toilets. Single level house, no basement.
What was once an occasional clog that required me getting out the plunger to fix, has now become noticeably more frequent with both toilets. The plunger does the job without much of a hassle, but I can expect another bout within a few days.
Any suggestions to try and narrow down the problem? Thank you.

What type toilets did you replace the old ones with? There is a flush factor on most toilets, one through 10, 10 being the best. I ask this, because I replaced two in our house not knowing this factor. Although I was looking for ADA height and low flow, I didn't pay attention to the flush factor, which was only 2.5. They suck at best. I plan on pulling them and replacing with a much higher rated brand/style, and using the old ones to grow tomatoes in, probably.

One is a Kohler, the other is an inexpensive model I picked up at Home Depot. I think it is called Toilet-in-a-Box, or some such thing. :o That said, how do I find out the flush factor?
And from what I recall, when these toilets were installed back when, they didn't have this issue.

Check on the displays at HD. You will see a flush factor beside each model. Had I seen this, likewise, I would have bought differently. Of course the better it flushes, the better HD gets paid, so beware. I'm changing mine out asap.

Im wondering if instead of the problem being the toilet itself could you actually have a clog in the main line draining from the house to your septic or sewer system? If the toilets are only clogging intermittantly and you dont note that the waste that is causing the clog is the variant then its probably not the toilet itself. You could have roots growing into your drain line causing or something else down stream, so to speak, that is causing the problem. If you are a proficient DIY'r you maight try an aggressive snaking of your drains from the toilets out.

I suspect it's a line problem rather than the toilets. Since both are acting up, it's unlikely the toilets are the cause.
Assuming this reasoning is correct, what are my options for this problem? I am not a competent do-it-yourself type, which means hiring out a pro. Are we talking a roto-rooter type service? If so, any ball park figures on what this might cost? Thank you.

A local plumber should be able to do the job. Roto Router is an option but many find them more expensive. Your other option would be to go to the local tool rental store or HD if yours has tool rental and rent a 25' "snake". The store will show you how it works. Locate the clean out opening on your house which is usually on or near an outside against the housel and clean the drain yourself. It is work but not beyond the efforts of most guys.
Good luck you can do it.