Mother using lockdown to stop kids from seeing dad

[Helmlover1]

So my partner’s kids (aged 14 and 17) have been told by their mother that because my partner is a key worker and still going to work they are not allowed to come round. My partner has tried to explain to them that even during lockdown kids of separated parents are still allowed to visit the non resident parent but they are still choosing to believe their mother, who incidentally has used every excuse in the book over the years to stop the kids from seeing their dad, so I feel she will be rubbing her hands in glee over this situation.

Is there anything we can actually do?

My eldest is not seeing his dad in lockdown.
Im not rubbing my hands with glee over it at all. Would be silly to mix households unnecessarily. Its not even a discussion.

Key worker doesn’t equal frontline
DH is classed as key worker but he’s a cameraman, works alone 80% of the time, 20% of the time he films an interview with a contributor in excess of 2m away, outside in the air which sweeps particles away. Zero contact. When he’s not on a deployment he’s at home, so I reckon in an 8 hour shift he is at home for 5-6 of those hours.
His ex has stopped contact without his agreement, even though no one is high risk, and he’s explained he’s not working in an office, a supermarket or a hospital. There’s literally a higher chance of catching something going to Tesco than there is doing his job!

14 & 17 can make up their own minds
That. If they are not coming, it's because they don't want to not because of what their mum is telling them although it is easier to believe that this is the case.