Jam question... want to make seedless mixed berry

My Mom is 85 and she is the jam maker in the house. Sometimes she mixes a couple fruits... such as she just made Strawberry/Red Raspberry. She uses 3/4 strawberries to 1/4 red raspberries. She forgot to sieve out part of the seeds.

I HATE seeds. I have a texture thing about foods, and skins and seeds - well, I just can't deal with them. Such as, I love tomatoes, but I take out all the seeds and jelly stuff or I can't choke them down. LOL

We have a quart of red raspberries left that we froze. I am wondering if we freeze some strawberries now while in season, if we could mix in black raspberries and blackberries when our wild ones are ripe.

Then - I would like to cook the fruit just a bit - enough to make sieving out the seeds easier.

She uses Certo.

If we use a recipe for blackberry or red raspberry, could we mix these fruits, sieve the seeds, and then measure the fruit....

Do you think there is a decent chance it would set up ok, or would it be a big waste of time, money etc. on a gamble that it **might** work?

I suggested we make jelly, but she says she has never made jelly, it is to much work, takes to much fruit, and she is not about to start now. If you have ever dealt with someone her age, there is no changing their mind. She lives with me, and I love her, but sometimes I wish she was a bit more flexible! '-)

Thanks!