Looking for Opinions on Whether to Add On, Stay Put, or New Build

Why not ask the parents if they would be interested in selling the office, since your trailer is getting cramped? BUY IT. Then it's YOURS.
I would not spend 10K to add on to a 40 yo trailer. And would it even be yours to sell someday since your in-laws own it (technically).

I feel these are bad ideas for family involvement (even if it is a good relationship--now):

1. Assuming that because you need more space, they need to accommodate you & your family-it is, after all their house, and they may want to stay just the way they are--home and office and your family in the trailer. They are already providing rent/payment free living. Don't look for more.
2. Don't put all of your eggs in the same basket. Will you want to stay there forever? Do you want to move off of the property eventually? Do you plan to wait until they are too old or infirmed then inherit all of the property?

If it was me, personally, I would sit tight, deal with the room issue (no 3rd bedroom--no negotiation) and keep socking away money to add to the down payment on your future home (new or pre-owned) so your mortgage is as small as possible, or nonexistent.

I suggest talking with your inlaws too. Maybe they have a specific line of thinking but don't want to bring it up if you currently do not pay rent but they would want you to if you moved into the office.

My second comment is I wonder how your children sleep in the room? I have a 3 and 1 year old who share a very small bedroom and I envision a twin bed with a trundle that pulls out to give them the most room (think it's a 10x10 room) once my son is out of a crib. What type of bed do your kids share?

Good luck!

Good Morning M., I don't want to sound morbid or uncarring, but who is your fil leaving his house and land to? what you describe sounds great. I think it would be fun for you guys to build a house on your fil land if he approves. I think men like us to approach things with others because we have more tack, we can explain better, get the point across quicker so don't look at that in a negative way. Siblings that age should not share a room, I think changing that as soon as you can would be best. Don't argue with your husband we catch more blessings from our husbands by being sweet and loving than apposing them. Hope it all works out. J.

Updated

Good Morning M., I don't want to sound morbid or uncarring, but who is your fil leaving his house and land to? what you describe sounds great. I think it would be fun for you guys to build a house on your fil land if he approves. I think men like us to approach things with others because we have more tack, we can explain better, get the point across quicker so don't look at that in a negative way. Siblings that age should not share a room, I think changing that as soon as you can would be best. Don't argue with your husband we catch more blessings from our husbands by being sweet and loving than apposing them. Hope it all works out. J.

Hi M.,

You could give your son the master bedroom. You and your husband could sleep in the livingroom. That suggestion might cause some action. How big is the master bedroom? Can it be divided into 2 bedrooms - one for each child, and make the children's bedroom the master bedroom? How big is the livingroom? Can you build a wall there to make a child's bedroom?

Too bad you can't all live in the house. Plenty of room there.

Would it really cost 10k to build an addition? That sounds awfully high.

Good luck,
: ) M.D.

I agree with your assessment of adding on to the trailer. Don't what a waste of money.
This request of your son, however, is a perfect opportunity to engage your in-laws in the discussion of "what next?" for all of you in terms of living situations.
I would sit down with them (all adults, no kids) and indicate that you need their help in this situation. Lay out the request and the realities you mentioned above. Let them know you are speakin to them because you value and respect their thoughts , but also that knowing their feelings/intentions/desires will help you all make the next step in your lives. Be sure it is a frank conversation about the living arrangements, no relationships, etc. I don't know how touchy your in-laws are, but hopefully approaching them with honesty and respect can help you all make a smart decision.
Best