Neighbours not using parking space

[BrimFire]

New build estate with one allocated parking space per house. We all have two cars in our terraced row.
At the end of the allocated space ithere is enough for 2 cars if parked well. There is also room for 2 cars on a short pavement ( it doesn’t go anywhere and isn’t used by people). This is shared by those in the flats.

We have just got new neighbours. There house faces the end and they have 2 cars and a van. They park on the pavement just outside their house double parking with those opposite. They also put the van on the end of the spaces but taking up both. They don’t park in their allocated space.

Another neighbour has been round to ask if they knew it was theres and they said they yes and they were using it. There has been a car in there once but never overnight or in the evening. So we’ve lost 2 spaces and the entrance is now difficult to use.

AIBU to ask them to use the space given or can they park where they want as theres no restrictions.
Question mark is their allocated space.

Is there some part of "If a bit of public road is legitimate to park on then it's legitimate for anyone with valid road tax to park there and local residents do not get to say who" that you don't understand? I don't know how to put it more simply. There is no right for any specific member of the public to have parking priority over another, it is all first-come-first-served. The only way to get a legitimate right to easy parking by your home is to live somewhere with suffient garage, private driveway or allocated parking spaces to accommodate the vehicles you have on dedicated land that you have primary rights over. If you aren't doing that then you have no right to expect any concessions from anyone who also wants to use that public space. You could campaign for the establishment of a resident parking permit zone which are sometimes established with rules that exponentially increase the costs per permit of each additional vehicle per household that discourage multi-vehicle households, but the spaces would still be first-come-first-served. If person X likes parking in a particular space and that space is available, but for some reason chooses to leave it empty so that person Y can use it, the chances are that person Z (or entirely unrelated persons A/B/C) will come along first and take the space so neither X nor Y get it, it's a pointless kind of virtue-signalling to pretend that such a gesture would be sensible.

I'm not reading all that. I didn't mention the right to park there because that was indeed valid. I responded to a point you made that wasn't at all valid.