Lots of people had a photo of themselves on their gravestone
Yes, it is quite popular here.
Russians who live in Latvia definitely ought to make a serious effort to learn Latvian unless they have a very solid reason not to (like if they are very old or have a learning disability). It is disrespectful and arrogant not to.
Russians who are not prepared to respect Latvia should move somewhere else.
Completely agree.
But there are people who do not respect this country, and also do not want to go anywhere else.

the staff at the office refused to speak Russian with her, even though they knew it
As I said - many people (me included) can understand Russian well, but speaking and writing is another matter.
In Latvian schools they do not teach Russian as mandatory subject anymore.
I have no idea what this was about.
It is Latvian Legionnaires cemetery.
Latvian Legion members were forcibly conscripted by Nazi Germany in 1943 and sent to fight Red Army.
Some extremists claim that they participated in Holocaust, which is false, because all jews in Latvian territory were exterminated before 1943.

But soviets also forcibly conscripted latvians in the Red Army and sent them to fight Latvian Legion and other German forces.
It was a real tragedy - brothers were forced to fight against each other - another reason why 9. may is nothing to celebrate for.
The view that the USSR liberated Latvia which then more or less voluntarily entered the USSR (which incidentally I more or less believed while growing up) is simply not something that normal Latvians agree with.
Yes, because it is Soviet propaganda - my grandparents didn't voluntarily deport themselves :P .
Clearly it's either banned or strongly discouraged.
It is banned by the law - you can be fined if you don't comply:
(4) Information included in statements, signs, posters, placards, announcements or other notices, if it affects the lawful interests of the public and is intended for public awareness in places accessible to the public, shall be provided in the official language, except in cases prescribed in Paragraph five of this Section.
(5) Observing the purpose of this Law, and the basic principles for the use of language contained in Section 2 of this Law, the Cabinet shall determine cases where a foreign language may be used concurrently with the official language in information that is intended for public awareness in places accessible to the public.
By the Official language law - Russian is regarded as a foreign language.

There is a mechanism for adding or removing official languages in our constitution (Satversme).
The only way to do this is through a referendum.
At least half of all voting age citizens must take part, and at least half of all voting age citizens MUST vote "FOR".
This means that at least ~750 000 citizens need to participate in this referendum and all of them need to vote "for".
But since Russian speaking Latvian citizens are only about ~300 000 and also ~300 000 non-citizens - Russian will not be an official language anytime soon.
4. The Latvian language is the official language in the Republic of Latvia. The national flag of Latvia shall be red with a band of white.
77. If the Saeima has amended the first, second, third, fourth, sixth or seventy-seventh Article of the Constitution, such amendments, in order to come into force as law, shall be submitted to a national referendum.