Aftermarket Heated Seating Wiring

Hello everyone! I am new to the forum. This is my first post. I am not very well versed in this field, so I am reaching out to you knowledgeable and friendly folks to answer a few questions.

I am installing heated seats in both the driver and passenger seats of a vehicle. I have the heating elements installed, but wanted to have another set of eyes or two look at my wiring plan and tell me if I'm doing it wrong or if I will be alright wiring them in this way.

From my photo (horrible drawing, sorry) you can see that the heating elements and switch are wired into a relay for each seat. My plan is to join the grounds & power wires coming in from each relay. The power wires both have an in-line 15 amp fuse on them. The consolidated power wires would be connected to the fuse box via an add a circuit fuse tap on an ignition fuse.

Questions
1) Am I safe to join both ground wires together into one wire with a connector and then secure that one ground wire to a good grounding source?
2) Same question for the power wires. Can I join them? If yes, do I need to keep the in line fuses since I'm tapping into the fuse box?
3) If I don't need the in line fuses, should I install a bigger fuse in the fuse slot I'm tapping into?
4) Would it be better for me to just jump into 2 separate ignition fuse instead of 1?

STOP

You need to power the heaters with a wire directly to the battery. Do not connect anything that draws 10 amps to an ignition source.

The ignition wire needs to be connected to the coil of the relay. Not the part of the relay that feeds the heaters. Ignition wire through a 1 amp fuse to the switch then to 86 of the relay. Ground terminal 85 of the relay.

Battery through 15 amp fuse then to 30 of the relay. 87 of the relay feeds heater.

Thank you for your quick response. I think most of that may already be set up in the wiring harness. I've attached a wiring diagram also. I assumed I could jump into the fuse box so that I could make sure the heated seating only powered up after ignition power is hot. After looking at this diagram, do you think I will need to add any additional wiring for the ignition, or simply wire directly to the battery instead of tapping into the fuse block?

When they say "we recommend drawing power via a relayed key-start trigger sourced directly from the battery."...

What do they mean exactly? From what I gather, they are suggesting tapping into the ignition relay under the hood next to the battery if possible? If so, do I just stick the wire under the pin as I reinstall the relay, or do they make some sort of jumper similar to the add a circuit for a relay?

Like I said, I'm not very well versed in this field. From the instructions I highlighted above I was lead to believe it was a simple plug into the fuse panel installation, but I didn't necessarily like that myself, which is what lead me here.

They are saying you should connect it as I suggested earlier.