Is a house left in trust liable for IHT

[NotaGonk]

DFiL died 10 years ago. He left his house to his partner (who I'll call DMiL even though she's not DH's mum). It was put into trust saying she could live there for life or sell it and use the proceeds to purchase another house. Upon her death the house would go to DH and his siblings.

DMiL sold the house and bought another to be closer to her grandkids. All fine. We went to visit her last week and she said she needed to "put her affairs in order" and that we should know that her assets (including the house) exceeded the IHT threshold and his siblings should expect to pay IHT on the house (worth about £250k). I'm a bit confused as I thought putting a house into trust made it exempt from IHT.

Anyone advice would be appreciated.

I thought their threshold was 325000, and even then you only pay on the portion over this amount.

She needs to take into account the transferable IHT from DFIL and the RNRB from him. I think all of this together may amount to around £950k (check out exact figures as RNRB is going up). Might take it out of IHT threshold? I’m not great on trusts but think it’s not that easy to avoid IHT through them.

You need a legal opinion. I don't think saying someone only has a life interest in a property is necessarily the same as formally putting it in a trust?
The IHT threshold can be as much as £950,000 if FIL didn't use his allowance as it passes on to MIL. So it may not be an issue anyway?

Thanks for replies. They weren't married so I don't think FiL could have transferred his allowance to her, could he?
What does RNRB stand for?

She has a house (from before she was with FiL) which she lets out so that takes her estate above the threshold.

I assume RNRB is residence nil rate band. You're allowed a higher threshold before IHT is due to allow for property (in v simple terms).

I'm not an expert and you need specific advice. I don't understand how you didn't pay IHT on his estate when he died as he wasn't married so not able to transfer under married person's allowance. For a married couple, both his estate and nil rate band allowance would transfer to the spouse and when the spouse dies, then the combined estate is subject to IHT, but with the double threshold before IHT due.

Trusts like these don't let you avoid IHT. Good forward planning does that!