Can I pay my husband's medical expenses from my HSA account when he is covered under his own insurance and he has a FSA?

[Opus 17]

Yes. Once you have money in an HSA, you can use it to pay for medical expenses for yourself, your spouse, and your dependents, regardless of any other medical coverage.

However, because the FSA can also be used to pay for medical expenses for the owner, a spouse, and dependents, your husband's FSA counts as "other medical Insurance" for you and disqualifies you from making contributions to your HSA.

If you made disallowed contributions, you need to remove them from your HSA, or pay income tax plus a 20% penalty. 

[Bsch4477]

Note that you can’t contribute to your HSA if his FSA also covers you.  
Yes, you can use your HSA to pay his medical expenses but if he loses his FSA money if he doesn’t use it, it would be better for him to pay those expenses. 

[Opus 17]

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@Bsch4477 wrote:

Note that you can’t contribute to your HSA if his FSA also covers you.  

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FSA's always cover the spouse, there's no "if". 

A "limited purpose FSA" does not count as other coverage, I should have mentioned that.  A limited purpose FSA can only cover certain listed expenses that are not covered by most traditional medical insurance like vision and dental care.