Your work load shouldn't double when your SS visits.  If your husband wants him to be with your family for more time during the summer, HE should be the one whose workload increases.  And HE should be the one who makes child care arrangements for his son while you go to your family reunion.  Your husband should prepare his son's meals if the kid is going to cry that he doesn't like your cooking.  Perhaps if HE had to do these things, he wouldn't be as interested in having an extra month.  Or perhaps he would, but your work load would not unreasonably increase.  It sounds like you have a lot on your plate and picking up his slack shouldn't be added to it.  I fully understand your husband wanting to have more time with his son, but he should not be overwhelming you to do so.

Ask your DH what his plans are for his son because he will be there to visit HIM. Make it clear that your summer is mapped out and that it will be up to him to entertain his child, not you. Not your child, not your responsibility.

If you want to see your mum this summer, go see her without DH & his kid. If you want to make plans on your time off, make them. You don’t have to include skid. DH does NOT get to decide for you what your plans are on your time off. If he wants extra time with SS that’s fine, but he either discusses it with you & you decide on a mutually beneficial arrangement, or he figures out childcare for his kid.

If you’re not happy with this, it’s up to you to draw boundaries for your husband. Take care of yourself. 

Please do not skip your family things because you feel obligated to take care of HIS child, after he made a decision that didn’t include you to take this kid for 3 months (don’t they have a custody agreement? How did he just made this decision and *poof*, it happens?). He will have to find care for his son while you are away at the very least He can also handle the work that comes along with him. You can stand up for yourself and tell your DH you don’t want to be responsible for him, this is your break too and spending it babysitting his son is a lot to ask.

Yep, I'm with the others. If he decides unilaterally that his kid has a longer visit, then he does the extra work, not you. SS can go to camp while DH is at work, and he can cook and do all the parenting for SS on the evenings and weekends, and he can take time off from work while you go to your family reunion.

If he can't see that's only reasonable, then you married a selfish jerk.   But start talking about it now.

DH needs to start planning.  Most camps where I live do not go three months, but many working parents piece together camps plus Y time.  If money is an issue, and dad will be taking the kid more than his alloted time, he needs to discuss child support with mom.  Now, many places have an equal amount payable every month, but it is caculated based on number of days at each house.  he needs to investigage.  

I skipped many fun weekends at my parents lake house because of not wanting to take my SS’s.  They are rude nasty jerks who I would throttle if they were snarky to my parents...so I just didn’t go. I would have had to take them alone since my DH works weekends....no way I was taking four boys anywhere alone.   

Then my father passed away suddenly and I was crushed.   I regret not spending those times with him so much.  I would give anything to go back and telling dH to figure out his own kids and have gone to see my parents.   

Dont let this time pass.  Tell DH they are his issue to handle and go soo your family.