DH unaware he is an Executor

I would think as long as your husband and sister agree they could hand it over to a solicitor to sort out for them. Of course it means they would have to pay but no hassle as such for them apart from signing things. This is what some close to me family executors did.

Unfortunately DH’s sister, who is older than him, is unlikely to agree to anything. It’s just her style. Their mother has always hoped they would get along but it’s virtually impossible as sister in law is very awkward and ‘bossy’. I guess MIL thought she was being fair naming them both as executors but had DH been informed he would have refused there and then.

DH and his brothers were joint executors of MILs will. To avoid complications the other two waived their roles, so that DH had sole control. However, this was agreed in a friendly manner.
Maybe getting legal advice might be the way forward.

If he doesn't want to do it, he should simply see a solicitor and sign a Renunciation form, which releases him from acting as executor. He needs to to this before his mother dies, if possible. This information is useful - www.co-oplegalservices.co.uk/media-centre/articles-jan-apr-2017/renunciation-as-executor-of-a-will/

If SIs-in-law is abroad is there nobody else available in this country?
My DD was Paws executor along with me but other than initially formally agreeing for me to deal with everything and co signing, she has not had to be hands on (and we were both happy with that as she lives 1 1/2 hours away, has 3 children and a demanding and inflexible job) ) We actually left quite a lot of the paperwork to my solicitor and she was really helpful.
Yes, you can have your solicitor named instead, but expect a considerably increased bill if they do it all.

Thank you stella1949. That’s very helpful. Followed the link and showed DH. You have made an old man very happy!

My DH was informed by his sister last year that he is one of the executors of her will. He wasn’t asked. She doesn’t work like that! I was very annoyed about it, and hope that, in the event, probate will be handled by her solicitor, as we live a 200 mile drive from where she lives, and I doubt the other executor will have the time to devote to it.

If he doesn't want to do it.DH and his brothers were joint executors of MILs will. To avoid complications the other two waived their role

Go to the CAB and ask. I am pretty sure there is a form you can complete when your DH's mother dies, or even before saying that you do not wish to act as executor of this will and you can then walk a way.