1: Clerics, paladins, and Druids know all class spells of all levels at the level they acquire spell casting.
2: the problem with the multiclassing rules is that they do not actually enforce their own sequential application/ because of how each Spells Prepared caster is actually worded in their function of preparing spells, the multiclass Spell Slots rule actually applies despite the Multiclass spells known and Prepared description because what you can prepare is based on what is your highest highest spell slots, which are not determined by your class level.
The rule says this:
it should say thisYou determine what spells you know and can prepare for each class individually, as if you were a single-classed member of that class. If you are a ranger 4/wizard 3, for example, you know three 1st-level ranger spells based on your levels in the ranger class. As 3rd-level wizard, you know three wizard cantrips, and your spellbook contains ten wizard spells, two of which (the two you gained when you reached 3rd level as a wizard) can be 2nd-level spells.
You determine what spells you know and can prepare for each class individually, as if you were a single-classed member of that class of which no other classes contribute their caster level to. If you are a ranger 4/wizard 3, for example, you know three 1st-level ranger spells based on your levels in the ranger class. As 3rd-level wizard, you know three wizard cantrips, and your spellbook contains ten wizard spells, two of which (the two you gained when you reached 3rd level as a wizard) can be 2nd-level spells.