Tvheadend

Yes and yes. When you map channels to services, you can have same-named services mapped the the same channel. If the service names aren't the same, you can manually assign services to a channel either through the channel editor or through the services tab.

As far as priority between tuners, this is handled in the DVB Inputs tab. On the pane where you assign a network to a tuner/adapter, there are also fields for priorities for both live viewing and recording. Set your preferred tuner to a higher priority.

If you to to Channel->Channels->map services there is a button "map all services". Here you can tick the box "merge same name". This will merge DVB-S and DVB-C channels that have the same name.

Priorities are in Configuration->DVBInputs. You may need to click "expert" to see "Priority" and "Streaming Priority". So you could increase priority for DVB-C, but it would still record on DVB-S if all DVB-C tuners were busy.

There is also Configuration->Stream->Stream profiles where there is a checkbox "switch to another service (on failure)" that you may want to tick in case DVB-S fails to tune it will failover and tune on DVB-C.

Thanks for the answers.
I'll think about to merge the channels.

Al