Ah dear, how I know that dilemma. Just too well actually
It was my main problem when things started with Lin. We are just like you and T, Lin was the new comer as well (kind of, as we knew each other for years already). We enjoy heated discussions, we play the same type of games, we love to fill our free time with chatting and playing. Sward (my husband) is quite often not involved in this kind of talk because he has slightly different interests. It has caused me quite some headache to figure this dynamic out and find solutions for the seemingly imbalance.
The most important step would be to get everyone together and talking. I tried to figure out what each could be thinking or needing and worried my self sick in the end. That is NOT the solution. You need to trust in your partners to tell you what they need and they need to remember to not rely on you to miraculously guess what they may be needing. This won't work. Communication is the most important part in such a relationship structure. As Ciel already pointed out
What I found to be helpful was the fact that they enjoy some similar things and spend some time together regularly. This helps balancing out the relationships and deepen the bonds everyone has with each other, because the friendly relationship they (may) have help relieve the stress you may be feeling (entertaining them and such) and grants you some free time for yourself as well.
As you asked what we like to do: My husband works most of the day and I can only be with him in the evening or on weekends. We therefore assigned a date-day just for the two of us. On Sundays we go out together, training in the gym, visit the sauna and sweatbath and just spend some time talking and relaxing with each other. We find this time for private connection to be quite helpful. Lin and I don't need those extra moments for each other, as we spend most of the day together and kind of 'do what we like to do with each other' almost 24/7. For the same reason Sward got an additional night every week (I switch beds/bedrooms every evening) to make up for the extended time apart in comparison to the time Lin and I have.
I have written about our transition to poly and living together in the life stories and blogs section (see link in signature). Maybe this could help to figure some things out. We stumbled about the concept of the love languages as well, you really should look into this, there is some helpful truth to be discovered for sure. Good luck
Facts: 30, female, bi, v-type relationship with Sward (husband, straight, mono) and Lin (boyfriend, straight, mono), poly-fi and co-primary.