My partner’s ex-in-laws lied about SOR Uncle who now has access to my partner’s 2 young children

[Learner1983]

My partner, who has 2 young daughters, recently revealed to me that his ex-wife’s brother is a convicted child sex offender.
This was due to the true nature and extremity of the original crime coming to light, which has for years remained somewhat hidden from my partner; ‘white lies’ were told and facts were concealed to paint the perpetrator as more of a victim, and my partner had naively believed them until now.
The ex-brother in law’s crimes and time served were spent a couple of years prior to the birth of my partner and his then wife’s 2 children, and so this man has been allowed to build an uncle-niece relationship with my partner’s two young girls, now only a couple of years younger than the age of his original victim.
(- He sexually groomed a minor online for almost a year before he was caught and served two years in prison.)

I have learned that although he is on the SOR indefinitely, as his crimes were over 10 years ago, there are currently no conditions upon him as he is not seen as a risk.
This is all very new to me and I am really struggling to get my head around how this is even possible that he would not be seen as a risk.

Since my partner is separated from his ex-wife/mother of the children, I am deeply concerned about how much access this ‘uncle’ has to the girls with or without supervision, and the reliability of my partner’s ex-in-laws in terms of safeguarding and protecting all parties concerned, given that they lied about his conviction, presumably to allow a relationship in the first place!

Does my partner have any rights legally to restrict or block the uncle’s access and how can this be ensured outwith his presence?

Is there anything I can do as I’m not an official guardian?

Can we contact the girls’ school and raise concerns without the mother’s knowledge?

I can’t describe how strong a need I feel in my gut to protect these two wee girls, and I am at a complete loss as to how to convey the extent of my worries to my partner who appears to have been lied to/had his head in the sand for the last 10 years.
I don’t know how to even begin to advise or support him other than being so angry!

Can anyone offer any advice on any aspect of this please?
Legalities or emotional support?
I’m feeling very overwhelmed.

My partner is also seeking a formal divorce from this woman at this time, and ‘doesn’t want to rock the boat’ … I don’t know if I should be pushing my partner to raise these issues of trust with his solicitor regarding care of the girls, or, if the girls appear to be safe, and nobody else has ever raised any concerns for their welfare, do I have to just let this go? (Whilst desperately wishing and praying that they are not at risk (and will never be at risk) from this man!!)