Your duties as guardian or conservator need not last forever.
But as you know best since you’ve been doing the job for a while now, a judge appointed you to serve because he or she was convinced that your father was not capable of managing his own finances or personal affairs.
In some cases, those involved can later go to court and plead and prove that an adult guardianship or conservatorship is no longer necessary. But those cases are rare.
If circumstances change, however, such as a remarriage as your dad is contemplating, it sometimes makes more sense to have another person appointed to serve, relieving the first of the duty. For example, the new spouse may become the new best person for the job. Or you may all agree that a neighbor or close friend might be best suited for the job. You could still volunteer to visit and help out your dad as you all saw fit, but the new appointee would be legally responsible for handling his money and affairs.
To get a substitute appointed, you need to file the appropriate forms with the court that originally appointed you. The court will then notify others who may be affected such as your siblings and may also hold a brief hearing to see whether anyone objects.
Since it sounds as if your family members are all on the same page with that, it should be a simple matter. Check your appointing papers for the court’s contact information or search online for its website; many provide all the forms you need, along with instructions for completing and filing them.