No, not currently. Maybe eventually.
Because Ordnance Survey have not released any of their footpath data as part of the OpenData scheme, the free maps instead use footpath data from OpenStreetMap.org. This data has been collected by volunteers and the quality and coverage is generally excellent, especially in popular walking areas - but it is not yet entirely complete.
If you have an iPod touch or a WiFi-only iPad, your device does not have a GPS. It is able to find your approximate location using nearby WiFi base stations, but this will only work in built-up areas.
You're probably only seeing the 1:25,000 free maps, not the 1:10,000 free maps.
First, check if you downloaded the 1:10,000 maps. If you view the "Map Management" screen areas with 1:10,000 will be shown in orange or yellow, or stripes including those colours.
If that is OK, check the "Scales" section of the settings screen. Check that the slider between 1:25,000 and 1:10,000 is not at the extreme right; if necessary, move it to the left.
If you delete and re-install the app, you will lose all of your waypoints, recorded tracks, and downloaded maps. So that should be an absolute last resort.
The first thing to try is the "Start In Safe Mode" switch. This is in the main settings app, under "UK Map". Turn this on and try to restart the app. If necessary do this a couple of times. This will cause the app to re-index your downloaded maps and reset your settings. This may be enough to resolve your problem.
Note that "safe mode" will hide all of your GPX files. They are not deleted, just hidden. Unhide them from the Files screen.
If you have a problem of this sort, and especially if it is reproducible, do please get in touch so that it can be investigated.
Note, however, that these categories are only approximations. The OpenStreetMap categorisation of paths and tracks does not correspond exactly to the Ordnance Survey conventions, and may not be perfectly accurate in the first place. Walkers will generally find that these paths are all open to them; cyclists and horse riders should be more cautious.
You can install and re-install the app on all your devices as many times as you like without paying again, as long as those devices are all associated with the same owner's "Apple ID".
The situation with "family sharing" is more complicated; I have tried not to enable this but Apple seem to have enabled it anyway, at least for some users. You may need to talk to Apple if you have difficulties related to this.
It's possible that my reply was categorised as junk by your email system. Check your junk email folder. I don't know exactly why this is, but presumably I am on someone's block list.
Yes, since version 4.3 you can use links of the form https://ukmapapp.com/map?coordinates, for example https://ukmapapp.com/map?NY21540721. The coordinates can be an OS grid reference or WGS84 latitude and longitude in the form 55.55N2.22W. Note that these only work as links, not if you type them directly into the Safari address bar.