I think the death registration you mention lends more strength to a mutiple birth occuring, several times either one or both of the assorted twins in my tree failed to survive.
Although you don't mention where and when i notice you have Lincolnshire rellies, the majority of my twin births are Lincoln and around 1905-1930, i have a dozen birth certs and 10 show a time, two don't, it's the date, place of birth and parents that prove the children are twins.
One set i can't say either way as i went for the death certs instead but again the address proves the connection as it matches another set of twins born 15 months before.