Mandatory fields - Can I turn Last name into a not-mandatory field?

I have a problem with our site. We have had to use the fields First Name - Last Name differently - as our membership-account holds one or two persons (a household). Person 1's name is entered into First Name - an eventual person 2s name (a spouse) is entered into Last Name. When there is only one person it causes problems (for example in event registration pro event-bookings) to the members that Last name is a mandatory field. Is there a way to make Last Name a not-mandatory field? If so, life would be so much easier.

Not sure if it'll work, but you can try editing the field within CB > Field Management and simply set it to not required.

Thanks, but it seeems to me that I do not have the option to make a predefined field not required. Or has I missed something to have this as a possibility?

You can make predefined fields not required. Can even set them not to display on profile and/or registration. You just can't disable them or delete them. Either edit the lastname field and set it as not required or click its green checkbox under the "Required?" column in CB > Field Management.