My husband and I, along with 2 other couples, are at the very beginning stages of planning a trip to Russia, what cities are must visit? We will likely be going the beginning of May. We will have a Russian with us for translation assistance but would prefer to not completely rely on her being around. Thank you!

Most travellers visit St.Petersburg and Moscow;
(Iam sure there are other interesting cities...)
English is spoken in high end stores ,hotels and restaurants
but not in many other places. Metro signs in Moscow are only in the Russian alphabet.

<< what cities are must visit?>>

None. The only places you ever "must" visit are peculiar to your desires.

The easiest will be Moscow and St Petersburg. There are plenty of others that are interesting but the two capitals (imperial and soviet/current) are closest to the other major cities in (the rest of) Europe.

Given the climate, you may want to investigate going later in May - St. Petersburg weather is notoriously rainy when it's not snowing and the city lies north of Juneau, Alaska. Early May can still be quite cool (if not cold).

Look at the Golden Ring, historic cities including Yaroslavl.

I'd say Moscow, Spb, Kazan. These three will give you a more rounded snapshot of Russia.

May is generally an OK time to visit, but a bit on the cold side. On the bright side, SPb is not going to be as insanely crowded with cruisers as later in the season.
There is a bunch of smaller historic towns available as day trips (or weekend cruises) from the three cities.
For the record, English signage is available I'm Moscow metro (as well as English-language announcements within the circle line); read up on transportation apps that will make getting around a lot easier.

"For the record, English signage is available I'm Moscow metro "

The station names were in Russian alphabet only when I was in Moscow a year ago.
Is the change recient?

It was in English when I was there last summer (for circle line only). From what I've heard, they had rolled it out to all stations within the brown circle line for the Confed Cup they had earlier this year.

The metro "layout schemes" located in individual metro cars have had English translation for years, but to see these you really had to stand close by (the font was almost transparent).

Overall, Yandex metro app is the way to go.