A tired terrier!???????
Does not compute Will Robinson!
My JRT is 12 yrs old. I "think" I saw him snoozing the other day so, just maybe he's slowing down.
The down side to terriers is they seem less inclined to pack structure then many other breeds. I've had good luck keeping multiple dogs together, even multiple males with bitches.
If ther temperment is sound any YOUR leadership skills are well honed then it's not a huge problem.
One problem is when the $#!+ hiits the fan even the ones you may think are low on the pole will happily jump in the fray. You best be able to have great voice control cause those little bassides are a LOT quicker then ANY 60+ lb dog and have more attitude them any of them.
For the OP's situation I'm not surre how well it will work.
Reason;
Your only going there on weekends with your dog.
I've had a couple of them that would jump a dog that had only left the yard with me for a few hours. I never got really excited because I could read that it was any kind of a "fight to the death" situation. Just a natural reaction to the little bassids. Maybe not natural but for sure not an UNnatural reaction for them.
An example;
I'm one of 7 kids. Most of us are doggy and our dogs go with us most of the time.
In the past, on any given Sunday at my mom and dad's house there may be 6-7 dogs. Bull Terrier, GSD, Flat coated Retriever, Norwich Terrier, Australian Shepherd, Border Terrier, mom and dad's mutt.
Anyone of us could be outside and never have a problem. We all read dogspretty well.
If nobody was going to be outside then one or more of the terriers would have to be put up, depending on whose was there. They just seemed to be drawn to one another's chip on the shoulder.
My only terrier now is the old JRT. He's NOT allowed outside without me, and me only if the GSDs are loose in the yard. I think he's actually afraid of the older GSD now but, being a terrier, he has no "Say uncle" in him.
Again, if YOUR leadership skills aren't top notch, don't leave them alone on these weekend visits.
Just a side note; When terrier racing first began there werer no muzzles. Once all the dogs were inside the finish line (hay bales) the $#!+ ALWAYS hit the fan. The "quarry" was gone and you've got 5-6 crazy little bassids going after one another.
The way they wer separated was with long electricialns gloves and a couple of 55 gal drums filled with water. You scooped them up and tossed them in.
You always ran across the one or three that wouldn't quit and they had to be held down...just a bit
.
There is a reason that the little bassids, JRTs in particular are called Min-Mals. The only difference is the JRTs don't have any environmental issues. You can stick two on top of a flag pole and they will argue about who hits the ground first when they jump off.
old dogs LOVE to learn new tricks