I did this spousal visa application 2.5 yrs ago (working on my FLR(M) now) but hopefully I can be a bit helpful. When I did it I was able to download & print out a blank version first so I could make a dummy copy to hand write out & refer to ---- not sure if it lets you do that now.
Anyway..... When I did this here's generically what I put
Family Details ---My Dad & Mom details...Where & when they were born, nationality etc
Medical Treatment --Me...Wants to know if I've ever needed/had treatment whilst over here on vacation & if I paid for it or did I owe money.
Sponsor Details --Spouse & their parents details....Where & when born, nationality, etc
English Language ---Me...Wants to know if I speak/read/understand English or will I have to take the test. I just put that my whole school career was in an English speaking environment in an English speaking system & English was my first language.
And back when I did it they wanted photo evidence of our relationship. If they still want photos, you just need to send 3 or 4. I did 1) First meeting in UK with month & date 2) A few yrs later in USA with month & date (was nice that my hair was longer) 3&4) Marriage with officiate in photo (friend took in the middle of the vows so could defo see it was a marriage ceremony).
Good Luck. Go into this knowing it's going to be stressful waiting to hear but don't despair! All the Experts here are very helpful.