multiple slow drains

Here are the details:

A 57-year-old single story house on a slab.

The sink and toilet in one bathroom drain slowly. The shower drain is fine. The shower drain through the p-trap was replaced a little over a year ago.
In the second bathroom, the toilet and bath drain slowly. The sink is fine.
Everything else is fine as well.

Is this a sign that the main sewer line could be clogged? Or something else?
If it is the main line, is this usually a job best left to a pro or could I tackle it myself? I’m fairly handy when pointed in the right direction.

Thanks.

I'm worried that your toilets only appear to drain slowly because of the type of toilets they are. Has their performance changed or have they always been like this?

If you are new to the house and just the bath and sink drains were draining slowly then I would suggest that this is just normal buildup (hair).

My sink and bath drains always slow over time and need to be cleaned about once a year or so (my wife has long hair). I use chemical cleaners for these (a whole bottle in each left over night) which most of the pros on here shy away from, but with a slow (rather than a blocked drain, which needs professional help) they work just fine for me.

One of the toilets has always been a problem in the 3.5 years we've lived here. The other toilet has been getting steadily worse over the last year.

The sink is an on and off thing. I can usually clear it for a time with compressed air or evil chemicals, but then the problem comes back over time.

The bathtub drain has slowly been getting worse as well.