How to best utilize my rewards points for trip to Europe?

I was sent this direction from r/churning, hopefully this is the right place to ask. I signed up for some rewards cards and have a bunch of points but now that I have them, I need to figure out how to best utilize them.

So, over the last couple months I have accumulated the following:

• ~43k SPG points

• ~90k United Miles

• ~17k American Airline Miles (I actually had these from prior to churning)

My goal(s), in order of priority are:

• 2 round-trip (economy or better if possible) tickets from Texas (either Austin, Houston, or Dallas - willing to drive if it makes sense) to Spain (destination Nerja) with a stop-over in Italy (Rome + Florence). I've found tickets for my dates in September through United for 60k United miles per person.

• If any extra points remain, a few free nights in a hotel in Rome, Florence, or elsewhere in Italy (if there is nothing left, I expect to pay for hotels/hostels/etc.)

My question - Can I somehow convert my SPG points or AA miles to United miles to pay for the 2nd ticket? If so, what is the best method to do it? If not, how can I get the most out of the SPG points?