There are a number of problems here:
(1) "You’re" is a contraction of “you are”. It should be changed to the possessive pronoun ("your").
(2) "Altar" is noun (describing a platform used for religious services). In this case, we want the verb ("alter").
(3) “Lay” is a transitive verb -- which means that it requires a direct object. In this case, we want the intransitive verb ("lie").
This can be really confusing because "lay" is also the past tense of "lie", while "laid" is the past tense of "lay". Here are some examples:
Present tense, transitive verb: "Now I lay me down to sleep".
Past tense, transitive verb: "Yesterday, I laid me down to sleep".
Present tense, intransitive verb: "Every day, I lie in bed until the sun rises".
Past tense, intransitive verb: "Yesterday, I lay in bed until the sun rose".
(4) "There" indicates a place. Try not to confuse it with the possessive pronoun ("their"). In this case, however, you want the second-person pronoun (not the third): "your".
(5) "Too" is an adverb of intensity. To produce the infinitive form of a verb, we need the particle "to".
2. Apostrophe use:
An apostrophe signals possession or a contraction. Plural nouns do not have an apostrophe before the "s". Also, when a noun is used as an adjective, it cannot change its form, e.g. "dinner party".
"You …your brothers…your sisters" is a plural subject, so the verb must be plural, too ("need").
4. Infinitive vs. gerund:
In this sentence, we need the infinitive (not a gerund) after "need": "need to alter …and to be".
If "clean", "preparing" and "make" are construed as items in a list, they should have a parallel construction, which means "preparing" should take the same (infinitive) form as the other items. And because of the parallel construction, the particle ("to") can be omitted after the first use.
If "preparing" is construed as an explanation for the activity, we might want to say something like "in preparation for".
5. Parallel construction:
Again, because of the parallel construction, we can omit the phrase "you will have to" before "make".
6. Article use:
It's not just any house that needs to be cleaned but a specific one (their house), so we should use the definite article ("the") instead of "a".
7. Unnecessary word:
"Watching TV" is not meant to describe the purpose of "lying on the couch", so we do not need the preposition ("for").
We don't need to insert comma before the first coordinating conjunction ("but") since it doesn't join two independent clauses -- but we should insert one before the last ("and") since it does join two independent clauses.
Not only you and your brothers but also your sisters need to alter your plans and be home early to clean the house, prepare for our dinner party, and make the appetizers instead of lying on the couch watching TV.