5th level spells require 5th level (or higher) slots, unless it is a ritual spell.
The rules for Spellcasting state:
When a character casts a spell, he or she expends a slot of that spell’s level or higher, effectively "filling" a slot with the spell. You can think of a spell slot as a groove of a certain size — small for a 1st-level slot, larger for a spell of higher level. A 1st-level spell fits into a slot of any size, but a 9th-level spell fits only in a 9th-level slot. So when Umara casts magic missile, a 1st-level spell, she spends one of her four 1st-level slots and has three remaining.
So you are unable to cast spells for which you do not have sufficiently large spell slots. To cast a 5th level spell, you must have available a 5th level (or higher) slot.
However, if you are able to cast ritual spells, then you can cast a spell as a ritual without expending a spell slot:
Certain spells have a special tag: ritual. Such a spell can be cast following the normal rules for spellcasting, or the spell can be cast as a ritual. The ritual version of a spell takes 10 minutes longer to cast than normal. It also doesn’t expend a spell slot, which means the ritual version of a spell can’t be cast at a higher level.
To cast a spell as a ritual, a spellcaster must have a feature that grants the ability to do so. The cleric and the druid, for example, have such a feature. The caster must also have the spell prepared or on his or her list of spells known, unless the character’s ritual feature specifies otherwise, as the wizard’s does.
This second paragraph is important: you must have a feature that allows you to cast spells as rituals to be able to do so. For example, the cleric's spellcasting feature states:
Ritual Casting
You can cast a cleric spell as a ritual if that spell has the ritual tag and you have the spell prepared.
The other exception here (besides rituals) would be if a feature allowed you to somehow cast a spell without expending a spell slot. For example, the Drow High Magic feat states:
You learn more of the magic typical of dark elves. You learn the detect magic spell and can cast it at will, without expending a spell slot. You also learn levitate and dispel magic, each of which you can cast once without expending a spell slot. You regain the ability to cast those two spells in this way when you finish a long rest. Charisma is your spellcasting ability for all three spells.
With this feat, you can cast detect magic, levitate, and dispel magic even if you don’t have spell slots for them, since the feat specifically says you can cast them without expending a spell slot. Since this Blood Magic homebrew feat only says you know these spells, you still need spell slots to cast them.
