I did my mums probate two years ago, the forms are very straightforward, especially with a will and husband as beneficiary.
Your DH and yourself can both remain as executors, or one of you can relinquish the role (again this is part of the form). If you both stay, you both need to sign the oath, but its not a problem. My DB and I both stayed as executors, even though I did the work, as he can be awkward and I didnt want any come back!
Yes you will need the will, and valuations of anything she owned that wont automatically go to her husband eg money in sole bank accounts, I think joint account money will just automatically be his.
With house, assuming there is one, again it depends how it is held, which you can find from deeds or land registry. If joint tenants, both own the whole home, so her DH will automatically be the owner now and it wont need to be listed for probate. If tenants in common, she owned half and that half will need to be valued for probate.
Once probate form has been sent off, you will get a letter within a week or 2, for you to sign an oath. This can be done at a solicitors office, or at a probate office. All info is easily accessed online.