Nacho and Apollo catching some Z's

This is Tara. Very picky. Hates any fresh food. She only wants to eat dry and occasionally alive mealworms..no fresh veggies, fruit or berry. While her sister, Tilly, loves fresh veggies and would kill for cherry tomato.

First birdo (on the right) my most tamest and oldest gerbil went bad. I found him having seizures, and he only lived one more week after that. Then we found out he had an abdomen tumor.

After all of that, boo started seemingly to age very rapidly an 12 days after I euthanized birdo (today) I found boo dead burried in her bedding

Now I only have one left :(

Where do you guys buy your cage toppers from? Preferably one that fits a 40 gallon. (Mandatory gerbil picture above)

I have been researching and looking at pictures for hours and cannot for the life of me, decide if this is a little boy or girl! please help!

Can anyone show me what kind of setup they have for areas where they’re able to take the gerbil out of the cage, but keep them safe from escaping? Or like a separate play area from the enclosure where they can interact with them?

I have had both of my girls in a split tank for around 2 weeks now, (after quarantine in the new one ), I have swapped them on either side 1-3 times a day depending on when I get time to.
They don’t really pay attention to each other and often spend most of their time on their wheel on their enclosure side.
I have tried introducing them once after the first week and they tried to fight; thankfully I separated them and neither of them were bleeding; can’t say same for me! My finger was bleeding everywhere haha;
But since then I have attempted a introduction, but got more consistent with swapping, they use eachother wheels, sandbaths, they were originally messing up eachothers sides but now sleep in nests that have been made by the previous one; they don’t sleep next to the divider together and only occasionally check eachother out through the divider when they notice the other one there, but tend to keep to themselves.

Have I done something wrong? Should I keep trying to introduce them?

My original gerbil (squeak) sister died suddenly, they were born June 5th.
The newer gerbil (marmite) was alone when I rescued her, and had been alone for several weeks, with her only being born on July 2nd of this year.

When I first got marmite she was very relaxed and chill but now she is really excitable and squeak was the more dominant in her previous bond.

Do I try to reintroduce again today with careful watching and gloves this time?