I would look at how much you could get for each property first. If you split the profit 3 ways (after all the fees involved with selling), would you have enough to buy a new place, make any necessary repairs, and have some money as a buffer to pay the mortgage in case you can't get a tenant right away or something big breaks? Or do you have enough to buy another place with cash?
Also, it's important to note that if the houses you have are already free and clear, you'd be making almost pure profit (minus repairs and taxes) off of rent, and if it stands vacant you don't have to worry about where you're going to find the money to cover the mortgage.
I've had good experience working with family, but there is the risk of damaging your relationship with your brother if it doesn't work out. If you do rent it out with your brother, write out an agreement beforehand outlining exactly who is responsible for doing what - who answers the tenants' calls about the broken toilet, who makes repairs or finds a repairman, who collects rent, etc. AND how you will divide income. If you are doing twice the work, it's fair that you would get 2/3 of the profit (which might also satisfy your husband's concern), but that's something to negotiate.
One last note - if this was left to you and your brothers, your husband would not get a cut of the profits. If you and your brother decide to divide the profits evenly, it's a 50/50 split, not a 33/33/33. Be fair, don't (even inadvertently) cheat your brother, and remember your relationship is more important than money matters.
Good luck!
