Both of those sentences have some grammatical errors in them. I suspect that, when you say it's "schoolwork" but not homework, these aren't from a specific source, but your own attempt at writing these.
This isn't necessarily bad, but we need to address the parts that are incorrect, why they're incorrect, and some additional information that will aid you in long-term understanding.
Let's start with the first example:
There are a number of items here that are not correct. Please see the correction below:
I've put in bold the corrections to the issues in the sentence:
- Even though it is pronounced え, the particle is written with the へ kana.
- The particle を is used for an action applying onto an object. Liking something is not an object, so its use here is invalid. Here, you require the nominal の particle, to make the action "to go" into a noun-action "going". This, then, is followed by the が particle to express a subject (which is now 海へ行くの = "going to the sea").
As for the second example:
Let's take the same approach of correcting it first:
Here, the things to focus on are these:
- いえ行 is not a valid construction. Assuming いえ is for house, then you can use the word 家｛いえ｝here just fine. However, because the sentence is talking about "going often to grandfather and grandmother's house", you need to use the direction particle that you needed in the last example, which is へ (which is pronounced え as I mentioned before).
- 行 is the kanji for the action of going, but it is not in it of itself a complete verb word. The verb that is the actual verb is 行く, and needs to be conjugated based on what you're saying in your sentence. Assuming that the sentence is meant to say "goes often and stays (the night) there", then, you need to use the linking て-form for the verb 行く, which is 行｛い｝って.
- で is a particle that is used to explain how something happens by means of something else, so it cannot be used here when explaining the location at which something happens. That requires the location particle に instead.