Gold Kist is subpar for fresh eating, low sugar, bland, nonuniform ripening. Only good for jam.
With high summer heat, early ripening varieties should do better for you. Orangered is early ripening (first week of June here, likely late May in AZ), but it blooms with Blenheim. Orangered has the best flavor of all early apricots, but it comes slowly into bearing, you will need to wait a few years until it’s fully productive.
Tomcot is also a early ripening variety (end of May to early June here), but it blooms two weeks before Blenheim and Orangered, so will need another early bloomer to cross-pollinate. You can plant Tomcot and graft Nicole on it or vice versa and they will pollinate each other (they bloom and ripen at about the same time). Also can graft Apache to the same tree for additional cross-pollination and very early ripening fruit. When well pollinated, Tomcot is a very strong and consistent bearer, it produces a bumper crop year after year. Very nice looking, large, uniformly sized, clean fruit. Good apricot flavor, but compared to Orangered it’s relatively low on sugar. Nicole is also a strong producer when well pollinated.
Golden Sweet is a very high quality apricot, and it should cross-pollinate with Blenheim (actually they are both self fruitful, but additional cross-pollination never hurts). Unfortunately, it ripens just a couple of days before Blenheim, so does not provide much of an extension for the apricot season. I actually prefer Golden Sweet to Blenheim flavor wise, so I recommend at least adding a graft.
Tilton is late ripening (early-mid July here), so its ripening time will be during very high heat in AZ, I think this might be problematic.
Regarding the rootstock, Nemaguard is suitable for very well draining soil (which is common in AZ, but you should check that this is true for your backyard). I would not recommend using Citation unless you have very heavy clay soil. Citation tends to suffer in the summer if it does not get enough water, and with AZ heat it will never get enough water if your soil drains well.