My husband would like to work on the family tree with me. We opened an account for him, but can't link it to the existing record on my family tree - so he can't access or edit our info. Please help.
Your husband can view any profiles you have created for deceased persons. He will not be able to see your profile or the profiles of any living persons you have created.
The privacy of the living is protected in the collaborative FamilySearch Family Tree. He can create parallel/duplicate profiles for any living persons to connect from himself to the nearest deceased profile. He doesn't even need to add details or full names to create those profiles - just a nickname he will recognize. "Mom" or "Grandpa" with no further info is sufficient.
There's no way to give him access to his own info? No way to merge his new account with the existing one?
Not at this time, no.
Do not put info on live people. No one will see it. Only work on deceased people. Your husband will not only have to create his own person page which will duplicate the one you have for him, he will have to create a duplicate of you. Neither of you will see each other's page so don't spend time trying to add ANY info. I never add living people to the tree UNLESS they have asked me to work on their family history. Then all I do is grab a photo of them from their Facebook page and put it as their profile image so that when we have online meetings or I grab screen shots they can see where they are in the lineage.
You and your husband should work on your deceased ancestors.